326 DR. MARTIN BARRY'S RESEARCHES IN EMBRYOLOGY. 



change is seen in profile taking place. The gran ulous cords that are situated on one 

 side of the central mass have in this instance disappeared, while those on the other 

 side have become shortened, until the ovum has nearly reached the periphery of its 

 Graafian vesicle. And what is very remarkable, and an interesting instance of de- 

 sign, the particular part of the periphery of the Graafian vesicle to which the ovum 

 is thus conveyed, is always that directed towards the surface of the ovary. 



The Ovum at the 'perij)hery of the Graafian Vesicle\. 



86. Nor does the office of the retinacula end here. Having suspended the ovum 

 in the centre, and conveyed it to the periphery of the Graafian vesicle, they now re- 

 tain it in the latter situation (Plate VII. figs. 55 to 59. g^-X)- The central mass in 

 which the ovum is contained has become smaller, in many instances nearly of the 

 size and form of the tunica granulosa (^i), and in some animals appears more or less 

 distinctly circumscribed by a membrane §, a continuation of which invests the cord- 

 like, or at this period the band-like portions of the retinacula ||. The bandlike por- 

 tions of the retinacula have become reduced frequently to four in number, which are 

 at right angles to each other (figs. 58 and 59. ^^. Sometimes only two remain, 

 and I have met with more than four (figs. 56 and 57-^^.). The retinacula often seem 

 closely pressed against the inner membrane of the Graafian vesicle, for which pur- 

 pose, apparently, a portion of the membrana granulosa is in some instances previously 

 removed (figs. 57 and 59. ^.). In others the membrana granulosa is quite entire. 



8/. In Plate VII. fig. 61. is seen a fragment {g^) of the central portion of the reti- 

 nacula, from which the granulous bands have been broken oflf*|[ ; and fig. 60, pre- 

 sents the same part in situ, and of the real size, as viewed in a large Graafian vesicle 

 {h i) removed from the ovary, laid open, and its outer third reflected. 



88. In the determinate pressure of the ovum towards the periphery of its Graafian 

 vesicle, the retinacula obviously perform an important part-j~-j~. One eflfect of this de- 



t See the seventh column in the Table, page 304. 



X One of the figures now referred to (fig. 58. from the Ferret,) presents a curious resemblance to the eye- 

 ball "with nearly all its parts, including the four recti muscles. 



§ It is generally supposed that the surface of the "ovulum" (ovum) is in contact with the wall of its con- 

 taining cavity ; which however cannot be the case if the membrane now mentioned circumscribe the central 

 portion of the retinacula on all sides. 



In some animals that portion of this membrane which invests the central part of the retinacula is exceedingly 

 distinct, as for instance in the Cat and Dog. 



This membrane sometimes presents wrinkles or folds, as if susceptible of enlargement. 



II It is not improbable that a continuation of this membrane, reflected from the retinacula, may invest the 

 internal surface of the membrana granulosa (82. Note). 



^ Drawn as seen lying in a watch-glass. 



tt In fhe Dog the retinacula generally become at this period very obscure (Plate VIII. fig. B&. g^.), often 

 quite imperceptible ; and their central portion is reduced to a distinct membrane, closely investing the tunica 

 granulosa (fig. 66. gK and g^.) ; this membrane being, I presume, the "circular border" mentioned by Baer as 

 circumscribing his "disc" (tunica granulosa) in this animal. That the retinacula, however, though generally 

 iadistmct, and indeed invisible, in this animal, continue to exercise an influence on the situation of the ovum. 



