570 THE STRUCTURE AND DEVET,OPMENT 



and Muller's fluid are useless. Great difficulties have been ex- 

 perienced in distinguishing the artificial products of these 

 reagents. My investigations have led me to the result, that in 

 the gradual growth of the ova with the age of the individual 

 the changes are not quite identical with those during the rapid 

 growth which takes place at periods of sexual activity, after 

 the adult condition has been reached a result to which His 

 has also arrived, with reference to the ova of Osseous Fish. I 

 propose dealing separately with the several constituents of the 

 egg-follicle. 



Egg membranes. A vitelline membrane has been described 

 by Leydig 1 in Raja, and an albuminous layer of the nature of a 

 chorion 51 by Gegenbaur 3 in Acanthias the membranes described 

 in these two ways being no doubt equivalent. 



Dr Alex. Schultz 4 has more recently investigated a consider- 

 able variety of genera and finds three conditions of the egg 

 membranes, (i) In Torpedo, a homogeneous membrane, which 

 is of the nature of a chorion. (2) In Raja, a homogeneous 

 membrane which is, however, perforated. (3) In Squalidae, a 

 thick homogeneous membrane, internal to which is a thinner 

 perforated membrane. He apparently regards the perforated 

 inner membrane as a specialised part of the simple membrane 

 found in Torpedo, and states that this membrane is of the nature 

 of a chorion. 



My own investigations have led me to the conclusion that 

 though the egg-membranes can probably be reduced to single 

 type for Elasmobranchs, yet that they vary with the stage of 

 development of the ovum. Scyllium (stellare and canicula) and 

 Raja have formed the objects of my investigation. I commence 

 with the two former. 



It has already been stated that in Scyllium, even before the 

 follicular epithelium becomes formed, a delicate membrane round 



1 Rochen u. ffaie. 



8 By chorion I mean, following E. van Beneden's nomenclature, a membrane 

 formed by the follicular epithelium, and, by vitelline membrane, one formed by the 

 vitellus or body of the ovum. 



8 "Bau und Entwicklung d. Wirbelthiereier," &c., Mull. Archiv, 1861. 



4 "Zur Entwicklungsgeschichte d. Selachier," ArrJi.f. mikr. Anat. Vol. XI. 



