SECT. 9] PROTEIN METABOLISM 1103 



9*8. Protein Metabolism of Reptilian Eggs 



A group of Japanese workers has studied the development of the 

 marine turtle, Thalassochelys corticata, which lays eggs the size and 

 appearance of ping-pong balls in the warm littoral sand. Dealing 

 first with the end products of protein metabolism, Tomita reported 

 a preponderance of urea over uric acid. His figures were as follows, 

 both urea and uric acid being given as absolute amounts in milligrams 



per egg: Days Urea Uric acid 



45 24-5 0-15 



They lead to a typically aquatic nitrogen utilisation (see Table 163). 

 The preponderance of urea is curious in view of the uricotelic meta- 

 bolism of the sauropsida, but the nitrogen partition of chelonian 

 urine almost certainly does not follow the usual course in reptiHa, and 

 there is abundant evidence that the turtle ^gg is not a cleidoic 

 system (see Section 6-6 and the Epilegomena). 



The more general aspects of nitrogen metabolism were investigated 

 by Nakamura, who observed a diminution in the total nitrogen of 

 the eggs from 592 to 506 mgm. per egg. This is very interesting in 

 view of Tomita's findings, for the egg of this turtle thus not only 

 absorbs water from its environment but also gives off end-products 

 of nitrogen catabolism to it. Transition from ureotelic to uricotelic 

 habit occurs, then, not between amphibia and reptiles but between 

 Chelonia and Sauria. The following table shows the movements of the 

 nitrogen within the €:gg according to Nakamura's analyses : 



