CHAPTER VII. 



AMPHIBIA 1 . 



THE eggs of most Amphibia 2 are laid in water. They are 

 smallish nearly spherical bodies, and in the majority of known 

 Anura (all the European species), and in many Urodela (Am- 

 blystoma, Axolotl, though not in the common Newt) part of the 

 surface is dark or black, owing to the presence of a superficial 

 layer of pigment, while the remainder is unpigmented. The pig- 

 mented part is at the upper pole of the egg, and contains the 

 germinal vesicle till the time of its atrophy ; and the yolk- 

 granules in it are smaller than those in the unpigmented part. 

 The ovum is closely surrounded by a vitelline membrane 3 , and 

 receives, in its passage down the oviduct, a gelatinous investment 

 of varying structure. 



In the Anura the eggs are fertilized as they leave the oviduct. 

 In some of the Urodela the mode of fertilization is still imperfectly 

 understood. In Salamanders and probably Newts it is internal 4 ; 



1 The following classification of the Amphibia is employed in the present chapter: 

 fAGLOSSA. 



I. Anura. {PHANEROGLOSSA. 



( Trachystomata. 

 PERENNIBRANCHIATA \ Proteidce- 



ii. Urodela. 



CADUCIBRANCHIATA /AmphiumiiUv. 



{Menopomidre. 



( Amblystomidae . 

 MYCTODERA <,, , , ., 



^Salamandndse. 



III. Gymnophiona. 



2 I am under great obligations to Mr Parker for having kindly supplied me, in 

 answer to my questions, with a large amount of valuable information on the develop- 

 ment of the Amphibia. 



3 Within the vitelline membrane there appears to be present, in the Anura at any 

 rate, a very delicate membrane closely applied to the yolk. 



4 Allen Thomson informs me that he has watched the process of fertilization in 

 the Newt, and that the male deposits the semen in the water close to the female. 

 From the water it seems to enter the female generative aperture. Von Siebold has 

 shewn that there is present in female Newts and Salamanders a spermatic bursa. In 

 this bursa the spermatozoa long (three months) retain their vitality in some Sala- 

 manders. Various peculiarities in the gestation are to be explained by this fact. 





