The Tetrapoda: Amphibia, Reptiles, Birds 605 



in a manner similar to that utilized by the mammals; noteably, by 

 changes in the partial pressure within the coelomic cavity. Since 

 the reptiles are without diaphragms, other muscles of the turtle per- 

 form this function. Muscles located in the region of the legs and be- 

 neath the viscera when contracted enlarge the coelom and air enters 

 the lungs. Expiration is brought about by the contraction of two 

 pairs of ventrally located muscles which push against the viscera and 

 thus forceably expel the air out of the lungs. 



The turtle despite having large lungs and an excellent ventilating 

 system has but small need for a large oxygen supply inasmuch as 

 its metabolism is very low. This, however, has certain advantages, 

 for the turtle can make a single inspiration supply enough oxygen for 

 two or more hours at a time. Some of the aquatic turtles further aug- 

 ment this pulmonary respiration by pharyngeal and cloacal respiration. 

 The pharynx is highly vascular, and the turtle is able to suck in and 

 expel water into this region and bring about some respiratory ex- 

 change. Similarly, there are two thin-walled, vascular sacs connected 

 to the cloaca. Water may be pumped in and out of these for further 

 respiratory exchange. 



Turtles have internal fertilization with sperm transference accom- 

 plished by means of a copulatory organ. The eggs are laid in soil, 

 sand, or under debris and are left alone until they hatch. The young 

 turtles are left to their own devices for .survival. The aquatic forms 

 usually hasten to the nearest water. In northern areas, turtles hiber- 

 nate during the winter months. The aquatic forms hibernate in the 

 bottoms of streams or ponds while the terrestrial forms often burrow 

 into soil or under piles of debris. 



Though the turtles have retained essentially the same form during 

 their long geologic history, a number of different types have evolved. 

 Some of these types include the heavily armored box turtle, Terrapene; 

 the snapper, Chelydra; the slider, Pseudemys; the painted turtle, Chrys- 

 emys; the soft-shelled turtle, Aniyda; the gopher turtle, Gopherus; and 

 the various sea turtles such as the green turtle, Chelonia, the diamond- 

 back terrapin, Malaclemys, the hawksbill, EreUnochelys, and the log- 

 gerhead, Caretta. 



Terrapene (Fig. 202, d) is a common inhabitant of moist wood- 

 lands and gardens and is easily recognized by its arched yellow-marked 

 carapace and hinged plastron. It feeds on both insects and vegetation 

 and is often considered quite an asset due to its destruction of harmful 

 insects. The snapper, Chelydra, has a very weak plastron coupled with 



