ZONA PELLUCIDA IN TURTLE EGGS 241 



trary to his earlier opinion, as a product of the ooplasm, while 

 Rubaschkin favors the view that it is derived from the epithelium. 

 Of those who express an opinion on the zona pellucida of the 

 egg in vertebrate groups below the mammals there may be cited 

 Lams on the European smelt (Osmerus eperlanus), Munson on 

 the turtle (Clemmys marmorata), Waldeyer on selachians 

 amphibia, reptiles and birds, and Mile. Loyez on reptiles in 

 general. In Osmerus eperlanus, Lams ('03, '04) describes the 

 zona pellucida which he calls a chorion, thick and radially striated. 

 The striated appearance is due to innumerable canalicules running 

 perpendicular to the surface of the egg. Also, in the cytoplasm 

 of the egg directly beneath the yolk membrane, he sees granular 

 striations which "do not properly, in all probability, belong to 

 the egg cell but correspond to prolongations of the follicular cells 

 which have traversed the canalicules of the chorion and the 

 yolk membrane and become continuous with the cytoplasm of the 

 egg." Munson ('04, p. 331) states that in Clemmys marmorata 

 there occurs an egg membrane which is composed of two layers, 

 the outer homogeneous and the inner striated. In selachians, 

 amphibians, reptiles and birds Waldeyer ('01, '02, '03, p. 293) 

 shows that a zona pellucida consisting of an outer homogeneous 

 and an inner striated layer can be seen well only in developing 

 eggs, that it atrophies in mature eggs leaving only a very thin 

 egg membrane. The striated appearance is due to radial canals. 

 According to Mile. Loyez ('05, '06, p. 147) three membranes arise 

 in eggs of reptiles. The vitelline membrane which originates 

 directly from the primitive membrane of the oocyte is at first 

 very thin. As it increases in thickness it becomes finally striated 

 and then granular. The heavily striated zona radiata forms on 

 its inner surface early in the course of development. A very 

 transitory third membrane is differentiated from the internal 

 surface of the zona radiata. After its disappearance the inner 

 surface of the zona radiata becomes less and less distinct and 

 finally the striations come to appear in the superficial layer of 

 the egg. Mile. Loyez' vitelline membrane and zona radiata 

 together make up the zona pellucida, without doubt and her third 

 transitory membrane is the yolk membrane. 



