264 INEZ WHIPPLE WILDER. 



very large percentage of the brood. The large size of the eggs, 

 the certainty of fertilization which the internal method insures, 

 the well-sheltered position in which the eggs are placed, and the 

 maternal care during development are thus all conditions which 

 compensate for the very small number of eggs. 



Within the protective envelopes, the eggs orient themselves, 

 after the manner of amphibian eggs, with the animal pole above' 

 they continue this orientation until the embryos reach a suffici- 

 ently active stage to introduce other factors into the determi- 

 nation of their position in the egg. 



EMBRYONAL DEVELOPMENT. 



Without attempting to enter into the details of the embryology 

 of Desmognathus, certain general features of the course of develop- 

 ment of the egg are in place in an account of the life history of 

 the species. 



The early development of Desmognathus eggs has been worked 

 out by both H. H. Wilder ('04) and Hilton ('04 and '09). The seg- 

 mentation is found to be holoblastic, although, as demonstrated 

 by Hilton, the large size of the yolk mass prevents the complete 

 division internally until after the early blastula stage is reached, 

 thus placing the egg on the border line between the holoblastic 

 and meroblastic types, while throughout its entire development 

 the appearance of the embryo as it lies at first upon, and later 

 coiled around, the large mass of yolk cells, so strongly suggests 

 the condition found in meroblastic eggs that one instinctively 

 speaks of "embryo and yolk" (Fig. 5). This resemblance is 

 emphasized by the fact that the conspicuous capillary network 

 which early develops on the surface of the mass of yolk strongly 

 suggests the yolk circulation of meroblastic forms. Wilder ('04) 

 noted the correspondence externally of certain of these blood 

 vessels with the lateral cutaneous and median abdominal veins 

 of the adult, and on this ground did not consider them the homo- 

 logues of the vitelline veins of meroblastic forms. Piersol ('09), 

 on the other hand, describes a similar mesh work of blood vessels 

 in the splanchnic mesoblast of the embryo of Plethodon cinereus 

 erythronotus as a vitelline circulation, and as sections of Des- 

 mognathus embryos show the blood vessels in question to be 



