THE BIOLOGY OF THE CELL SURFACE 



Ascidians and Amphioxus belong to the chordates with- 

 out back-bone or vertebral column. Fishes, amphibians, 

 reptiles, birds and mammals are chordates with a vertebral 

 column. The lamprey is an example of the low vertebrate, 

 having no true jaws to the mouth as other vertebrates have. 



Fig. i6. — Egg of Pelrotnyzon fluviatilis (after Herfort). 



Its egg has been described by several investigators, among 

 these Calberla, whose beautiful work on fertilization of the 

 lamprey egg is classic. According to him this egg shows 

 regional cytoplasmic differentiation.' See also Herfort. 

 (Fig. i6.) ' 



For eggs of selachians (sharks and their allies), His has 

 written as follows: 



1 Calberla, iSjj; Bhhrn, iSSS: Herfort, rgoo. 



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