330 DR. MARTIN BARRY'S RESEARCHES IN EMBRYOLOGY. 



110. The retinacula consist of a central mass containing the ovum in its tunica 

 granulosa, and of cords or bands extending from this central mass to the membrana 

 granulosa. These structures at a certain period become invested by a membrane 

 (80—84.). 



111. The office of the retinacula appears to be. first, to suspend tlie ovum in the 

 fluid of the Graafian vesicle ; next, to convey it to a certain part of the periphery of 

 this vesicle ; subsequently to retain it in the latter situation ; and finally, to promote 

 its expulsion from the ovary (80 — 88.). 



112. The particular part of the periphery of the Graafian vesicle to which the 

 ovum is conveyed, is uniformly that directed towards the surface of the ovary (85.). 



113. The mass of granules escaping with the ovum on the bursting of a Graafian 

 vesicle under the compressor, is composed chiefly of the tunica granulosa and the 

 ruptured retinacula (64. 81.). 



114. The "cumulus" of Professor Baer is made up of the parts here called the 

 tunica granulosa and the central portion of the retinacula; and the band-like por- 

 tions, collectively, of what are here called the retinacula, mainly contribute to pro- 

 duce the appearance denominated the "flat disc" by that author (91.). 



115. In Mammals a thick and highly transparent membrane, the true chorion, is 

 formed external to the proper membrane of the yelk, while the latter is in the ovary. 

 The inner part of the substance of the chorion in its early stages is in a fluid state, 

 but it subsequently acquires more consistence. There is not any corresponding struc- 

 ture within the ovary of other vertebrated animals ; so that the body expelled from 

 that organ in the latter, is not (as in Mammalia) a true ovum, but a yelk-ball (52 

 —56.). 



116. The following appears to be the order of formation, as to time, of the more 

 permanent parts of the ovum and the Graafian vesicle, in Mammalia, viz. 



1. The germinal vesicle, with its contents (12 — 22.). 



2. An envelope consisting of oil-like globules and peculiar granules (14 — 16.). 



3. The ovisa«*, which forms around this envelope (23.). 



4. The yelk, which forms within the ovisac around the germinal vesicle (24.). 



5. The proper membrane of the yelk, which makes its appearance while the 



yelk is still in an incipient state (24. 49.). 



6. The chorion (24. 52.). 

 The proper covering or tunic of the ovisac {77-) ; and about the same time 



the peculiar granules of the ovisac arrange themselves (78. 79.) to form, 



fThe tunica granulosa (64.), 

 s The retinacula (80.), and 



I The membrana granulosa (72.). 



117. Such of these structures as are present in other vertebrated animals originate 

 in the same order as to time (27 — 47.)- 



