THE SYSTEMATIC ANATOMY OF A FCETAL SEA-LEOPARD. 241 



Compared with mammals, such as the pig, the adrenal of this Seal appears to 

 be somewhat behindhand in the relative rate of its development ; thus, in a pig 

 embryo of 119 mm. the medulla is well defined, and most of the sympathetic 

 derivatives are confined to it alone ; but in a pig embryo of 70 mm. the histology of 

 the gland is much as has been described above.* 



(vii.) The genital glands (PI. XXII. fig. 4). — As has been noted, the genital glands 

 in the present instance are ovaries ; each ovary has a well-defined histological appear- 

 ance, and it is possible to recognise — 



(a) An outer layer of rather high cubical epithelium. 



(b) A wide cortical zone composed of masses of rounded cells or primordial ova 



(some of these being considerably larger than others, and forming potential 

 ova which will later become surrounded by a follicle of smaller cells to 

 form the commencing Graafian follicles). Between the ova a good deal 

 of fibro-cellular connective tissue is to be seen, and this forms a dense 

 interlacing network supporting the egg-cells. 



(c) Deep to the above cortical zone comes a layer of fibro-cellular stroma, com- 



parable to the tunica albuginea of the testicle, but having a relatively 

 different position in the gland. 



(d) A central portion, composed for the most part of dense stroma, with here and 



there masses of ova, which are the remains of the so-called medullary 

 cords of somewhat earlier stages. 



In the mesovarium, which forms a wide peritoneal band of attachment, there are 

 to be seen mesonephric tubules and glomeruli, whilst at the point of attachment of 

 this band to the ovary there are some tubules, supported by stroma, forming the 

 rete ovarii. 



The above histological appearances correspond closely with those to be seen in 

 the ovary of a cat embryo of 94 mm. ; f no signs of developing Graafian follicles are 

 to be seen, as the follicular epithelium has not as yet been formed round any of the 

 larger ova. 



(viii.) The placenta (Text-fig. 2). — The details of the placenta and placentation 

 have been acquired in the present instance from the study of a specimen lent to the 

 author by Professor Waterston of King's College, London ; this specimen shows a 

 foetus of the Weddell Seal, a closely allied species, in situ in the uterus, with the 

 membranes in their proper relative position with regard to foetus and placenta. | The 

 relations of the amniotic sac to the foetus and umbilical cord are such that the 

 former appears to be enclosed in a small complete sac, which is quite closed towards 

 the ventral aspect of the embryo, the umbilical cord upon reaching the line of 

 closure dividing up into a number of branches each containing twigs from the 



* See Hertwig, op. cit. t Figured by Coert, Inaug. Dissert., Leiden, 1898. 



J Figured in Sir William Turner's Catalogue of Marine Mammals. 

 TRANS. ROY. SOC. EDIN, VOL. L. PART I. (NO. 8). 34 



