ORGANOGENESIS 



739 



Fig. 4. Excreted nitrogen per gram wet weight throughout development in black snake, 

 snapping turtle, chick and alligator embryos. The abscissa is calibrated in units of wet 

 weight rather than time because of the similarity in hatching weights between the pairs 

 as shown. Although the extremely high values at the beginning of development cannot 

 be shown, the trend is apparent, and the relatively high rate of protein degradation early 

 in development in each species is clear. 



The most striking features of the initial observations on the black snake (Clark, 

 1 953a) were : (j) 60% of the excreta in an incubation period of approximately 

 two months appeared in the form of urea; the balance was evenly divided between 

 ammonia, some of which escaped as a gas, and uric acid; (2) the total excreted 

 nitrogen of the embryo (7.0 g at hatching) was greater than that attributed to the 

 chick (approximately 40.0 g at hatching) ; {3) virtually all of the uric acid was 

 accumulated during the last week of incubation, and coincident with its ap- 

 pearance there occurred a decline in urea content; {4) urease activity was 

 demonstrated in the foetal liver and kidney at the time of urea decline, suggesting 

 a mechanism for conversion of uric acid ; (5) urea concentration in the allantoic 

 fluid rises to a maximum of 500 mg%. 



TABLE 1 



EXCRETED NITROGEN DURING EMBRYONIC DEVELOPMENT OF CERTAIN 

 REPTILES AND THE CHICK 



Species 



Alligator 

 Gartner Snake 

 Black Snake 

 Snapping Turtle 

 Chick 



Total Excreted JV (mg) Hatching Wt. (g) 



mg Njg Embryo 



15.28 

 2.52 

 12.55 

 1549 

 39.00 



36.0 



1-5 

 7.0 



9-3 

 39-00 



0.42 

 1.68 

 1.80 

 1.67 

 1. 00 



Literature p. 744 



