CHAPTER IX. 



REPTILIA. 



THE formation of the germinal layers in the Reptilia is very 

 imperfectly known. The Lizard has been studied in this respect 

 more completely than other types, and there are a few scattered 

 observations on Turtles and Snakes. 



The ovum has in all Reptilia a very similar structure to that 

 in Birds. Impregnation is effected in the upper part of the 

 oviduct, and the early stages of development invariably take 

 place in the oviduct. A few forms are viviparous, viz. some of 

 the blindworms amongst Lizards (Anguis, Seps), and some of 

 the Viperidae and Hydrophidae amongst the Serpents. In the 

 majority of cases, however, the eggs are laid in moist earth, 

 sand, &c. Around the true ovum an egg-shell (of the same 

 general nature as that in birds, though usually soft), and a 

 variable quantity of albumen, are deposited in the oviduct. The 

 extent to which development has proceeded in the oviparous 

 forms before the eggs are laid varies greatly in different species. 



The general features of the development (for a knowledge of 

 which we are mainly indebted to Rathke's beautiful memoirs), 

 the structure of the amnion and allantois, &c. are very much the 

 same as in Birds. 



The Lizards will be taken as type of the class, and a few 

 noteworthy points in the development of other groups will be 

 dealt with at the close of the Chapter. The following descrip- 

 tion, taken in the main from my own observations, applies to 

 Lacerta muralis. 



The segmentation is meroblastic, and similar to that in Birds. 

 At its close the resulting blastoderm becomes divided into two 

 layers, a superficial epiblast formed of a single row of cells, and 



