42 



CfllM^ROin FISHES AND THEIR DEVELOPMENT. 

 THE EGG AND ITS MEMBRANES. 



In the newly deposited capsule the egg measures 35 by 20 by 12 mm., but it is 

 smaller, together with the capsule, if taken from young fish (cf. the size of the 

 capsules shown in plate 11, fig. 10, and plate in, fig. 17), as is also the case in sela- 

 chians (Riickert). Its consistency becomes less fluid-like as development advances; 

 thus, shortly before breaking from the ovarian membrane, the egg has so little con- 

 sistency that it will flatten out to the diameter of about 45 mm. (jilate 11, fig. 5). 

 Its ellipsoidal outline is assumed when inclosed in the capsule. It will, however, 



Fig. 30. — Early ovarian egg ol Chimaera colliei. Seclion through major axis of egg. gs, Gonadial sinus; i,-?', germinative vesicle — 

 around it the extent of the space indicates the size of vesicle before fixation ; o, stalk attaching egg to ovary and inclosing the 

 arterial blood supply ; /, peritoneum ; /, tunic (^ granulosa). 



Figs. 31 and 32. —Sections of the marginal region of ovarian eggs (the first measuring about 5 mm. in diameter, the second about 15 mm.), 

 indicating changes in the tunic and the development of yollc. bm. Basement membrane (between the tunic and the egg); 

 by, botryoidal yolk masses developed in vacuoles in germinal yolk ; i, layers of connective and vascular tissue theca in ovarian 

 membrane surrounding egg; .^'.s', gonadial sinus; f, peritoneum; /.tunic of ovarian tissue inclosing egg (follicular epithelium); 

 /, inmost layer; m, middle layer; o, outmost layer; zr, zona radiata. X 585. 



present an almost spherical form (horizontal outline 25 by 20 mm.) if the constricting 

 capsule be opened (plate 11, fig. 8). In later stages it has the consistency of thick 

 cream. 



THE OVARIAN MEMBRANES. 



Comparison with corresponding stages in shark (Pristiurus) shows that the 

 wrappings of the ovarian eggs of Chimaera are the more complex. In earl}' stages of 

 the latter the ovarian tunic is thicker and its nuclear elements more abundant and 

 more evidently specialized. Thus in fig. 30, which shows in section an egg of about 

 5 mm., one notes the thickness of the tunic; this (greatly enlarged) is shown in 



