Acorn Worm

The acorn worms look like elongated worms with an acorn like head. The "acorn" is made up of a proboscis, or tubular structure, and a collar, into which the proboscis fits. The collar is attached to a long, flat, ruffled trunk, tapering toward the end. The animal ranges in length from an inch to four feet ; the average length is from six to ten inches. These relatively rare creatures are found on the Atlantic coast, buried in the mud and sand of the low tide zones. Like in the same way as in the vertebrates and is made up of the same tissue. Other authorities deny that the acorn worm has a chordate. They include the animal with the invertebrates, because it resembles them in many respects. The acorn worm's pharynx leads into the intestine, which is perforated with gill slits. The gills lead into a pouch, which opens to the exterior by gill pores. The intestine runs the length of the body. It ends in an anus at the tapered end of the trunk. The reproductive organs are located at the front end of the trunk. The sexes are separate; males produce sperm and females eggs. Fertilization takes place outside of the body after the sperm and eggs have been ejected from it. Some deep sea types, such as Hydrocephalus, reproduce asexually by budding. The larvae of acorn worms resemble those of the echinoderms (sea stars, sea urchins and their kin) in both structure and development. For this reason many believe that the chordates are descended from the same stock as the echinoderms. 
             

 shallow sea water one often finds orange, red or purple bearlike objects attached to rocks, piles and seaweed. These colorful "bags" are the primitive chordates In the adult animal, water bearing food particles passes through the mouth and is  filtered through gill slits. Food particles are trapped by the gill slits and enter the intestine. The water then flows into a surrounding sac  the atrium  and out through the siphon called the atrial pore. Undigested waste materials also pass out of the body by way of the atrial pore. Communicates can reproduce by budding. An adult buds again and again, producing new individuals. In time a large colony may develop on a rocky surface. Sexual reproduction also occurs. Communicates are hermaphrodites: that is, each animal produces male and female sex cells sperm and eggs. Fertilization may take place within the body ; or eggs and sperm may pass out of the body and unite elsewhere. 

Resort Climates

For a long time, many Europeans have placed much faith in the curative and restorative powers of clean air, sunshine, and pleasant weather. A 1964 report of the World Meteorological Organization in Geneva used phrases such as "climatic treatment" and "specific climatic therapy." It has been alleged that blood circulation, respiration, and skin condition are made health by exposure to favorable weather. These notions have resulted in the establishment of many health resorts in mountainous and southern-coastal areas. Baths in warm, sulfur-laden waters of certain natural springs are often part of the treatment. The benefit of the redolent waters and the air that surrounds them is debatable, but a week or two in a climatically optimal resort may send a city dweller home with a healthier mind and body. European climatologists have given a great deal of study to the most appropriate attributes of resort areas. To a certain extent, these depend on the purpose of the resort and the conditions of the people it seeks to attract. Generally, anyone seeking a pleasant period of recuperation from an illness is advised to avoid the following conditions: intense heat, particularly if accompanied by high humidity; polluted air, especially if the patient has had some kind of respiratory illness; highly changeable weather with frequent passages of fronts and cyclones; and excessively high elevations, where the presence of oxygen in the atmosphere may be too low. Sanatorium should be far enough from cities and industries to assure low concentrations of gaseous and particulate pollutants Local vegetation should be of varieties that produce little pollen. The clean, brisk air often found at moderately high elevations on the lee of a ridge or along a sea coast dominated by light sea breezes is recommended for summer resorts. On mountains or hilly terrain, spas are sometimes located in forest glades, where they are protected from strong winds by tall trees. Sunshine is considered therapeutic in many parts of the world. The World Meteorological Organization report, cited earlier, discusses the value of solar ultraviolet radiation in "hydrotherapy." These rays arc "used for their effects on skin cell metabolism, formation of substances such as vitamin I and detoxification processes." Hydrotherapy calls for long periods of exposure to the sun. Today, in the United States and a number of other countries, it is recognized that the risk of skin cancer through excessive exposure to sunlight exceeds the benefits of such exposure. In the Western Hemisphere, there is relatively little stress on health resorts, but a great many people migrate to the sunny south lands in winter. 

Comfort and Health

It is easy not to appreciate the full impact of the atmosphere on human well biophysical and psychological. Violent weather is obviously traumatic, causing injury and death to thousands every year; the effects of polluted air, though not so dramatic can still be tragic, particularly for the very young and very old with already existing lung problems. Sometimes the weather has such subtle influences that the hows and whys remain a mystery. For example, certain asthmatics find miracles in the desert air of southern Arizona while others find only disappointment, and the reasons for the differences still have not been found. It is sometimes difficult to specify in detail how the weather affects human behavior and psychological well-being, but there is no doubt that it does. Who can forget the joys of the first warm, sunny days of spring after a seemingly endless cold, gloomy winter? Also, it is well established that the strong, dry, gusty winds of the alpine foe and the California Santa Ana are associated with increases in abnormal behavior. No one needs to be told which weather conditions are physically pleasant and which ones cause discomfort. The most important element is temperature, but strong winds make cold days scent colder and hot days hotter and have many other effects as well. Even at moderate temperatures, atmospheric humanities affect human perception of air temperature. When the relative humidity is low, most people react as if the temperature were below its true value; when humidity is high, the opposite occurs. Investigations have been made of the losses and gains of heat by the human body as functions of temperature, humidity, and wind speed. Such information is particularly important in the design of clothing for use by people living and working in extreme environments . For example, the maintenance crews along the Alaskan oil pipeline must be protected from the frigid conditions that can cause frostbite or hypothermia. •

Aviation

Anyone who flies an airplane, a glider, or a balloon should take the weather into account before leaving the ground. Commercial and military pilots have ready access to the necessary information. Airplanes are designed to withstand the normal stresses imposed by violet weather events of the kind discussed in this chapter. Unfortunately there still are those rare circumstances where inclement weather, combined with pilot errors, leads to fatal accidents. The more a flier knows, through study and experience, the smaller the likelihood of such an episode. The major meteorological factors that affect an airplane in flight are wind, turbulence, lightning, hail, and aircraft icing (that is, the accumulation of ice on the leading edges of an airplane flying through a super cooled cloud). But weather considerations must begin at the runway. The length of runway needed for takeoff depends on the type and weight of the airplane, the elevation of the airport, the wind velocity, the air temperature, and the humidity. The lift imparted to an airplane's wings at any speed depends on the as density that is, the mass of air in unit volume of space which decreases with height. Departing airplanes must move faster in Denver (elevation about 5,300 feet) than in Chicago (elevation about 670 feet) to take off. To reach the higher speed, airplanes in Denver need longer runways. In addition, as the air temperature and (to a lesser extent) the humidity rise, the air density decreases; so longer takeoff runs are needed in summer than in winter. The altitude of an aircraft is usually measured by a pressure altimeter, which is calibrated according to the average pressure height relationship of the atmosphere.  Although labeled in units of altitude, the instrument actually responds to air pressure, which is a (unction of height. Since vertical distributions of temperature and density vary with time and place, so do the pressure at the ground and the rate at which pressure decreases with height. To take the deviations from average into account, a pilot adjusts the altimeter before takeoff and landing. Knowing the atmospheric pressure at the airport, the pilot sets the altimeter so that it reads the field elevation  when the airplane is on the ground. Up-to-date "altimeter settings" are normally supplied, via radio, from airport control towers. When air temperatures at flight altitudes are lower than the averages used to calibrate the altimeter, the actual altitude of the airplane is less than the one given by the altimeter; air temperatures above the averages have the opposite effect. Knowing the temperature, a pilot can easily compute a corrected altitude. Two important concerns in air travel are ceiling, which is defined as the height of the base of the lowest layer of clouds or other obscuring phenomenon that hides more than half the sky, and visibility, the greatest distance at which one can see and identify prominent objects. Low ceilings and visibility most often result from fogs or stratus clouds, but heavy snow or rain, blowing sand, or dense smoke and haze can also be causes. These conditions arc most significant during landings and takeoffs. In very dense fogs, ceilings and visibility can be nearly zero, bringing traffic to a halt. Fortunately, these "zero zero" conditions are not common. More often, ceilings are reduced to a few hundred feet and visibility to less than a mile, in which cases air traffic continues, though at a slower rate, in and out of airports having suitable radio or radar systems that can guide an airplane to a safe touchdown. Some types of fogs and low cloud layers form or become more dense on clear nights as a result of cooling by thermal radiation to the night sky. For this reason, ceilings and visibility may drop during the night and early morning. Pilots of small airplanes, who are often required to fly with the ground in sight, should schedule flights out of fog-prone airports for periods after the sun has burned off the fog and before fog begins to form in the evening or night.

Water And Vapor

Quite clearly, the results of farming depend on adequate and timely sup-plies of water. The critical factor is not rainfall but soil moisture throughout the life history of the crop involved. As everyone with house plants or a garden knows, the appropriate conditions depend on the plant species, the stage of growth, the properties of the soil, and air temperature and humidity. Water in the soil feeds and cools growing vegetation as it passes into the plant through the root systems. The flow of fluid transports nutrients into the stems and leaves. When the air is hot and dry, the tomatoes of the leaves open and a great deal of water vapor transpires into the air. In the process, the plant is cooled. In a sense, this is the vegetative equivalent to human perspiration. Because of uncertainties about the quantity and scheduling of watering needed to achieve optimum crop yields, irrigation practices have been less than maximally efficient. Vegetation can survive and even thrive in moderately dry soil, but when there is inadequate water, leaves begin to wilt. A heavy rainfall or deep irrigation will improve the health of the plants, but will not entirely undo the harm caused by the desiccation. This means, of course, that when irrigation is available, a grower should not wait for signs of distress; that is, the plant should not be used as a measure of water insufficiency. The crucial factor, soil moisture, should be monitored directly. A procedure widely recommended to the home gardener is poking a metal rod or digging a few inches into the soil to see if it is wet. Water should be applied when the soil is dry. Surprisingly, in arid regions, where irrigation is a necessary practice, ,a great many plants are killed by over-watering. This happens when an amateur farmer, seeing dry surfaces, incorrectly assumes that the dryness extends into the root zone. 

Commercial farmers sometimes use soil augers to gags the state of the soil. Another approach is to install electronic moisture sensors whose out-puts are recorded continuously. Some authorities believe these procedures are inadequate because they do not measure the wetness at enough points through a deep layer of earth. An alternative approach to the monitoring of soil moisture is to maintain a water budget of the cultivated field. This involves measuring the water added by precipitation and irrigation and balancing it against the water leaving the field by evaporation and transpiration. This requires computation of the last two processes, which are often lumped together and called transpiration.