igiQ-] 1^- Southwell & B. Prashad : Studies of Indian Fishes. 229 



dorsal and to the right of the colon ; it is connected with the 

 external yolk-sac through the yolk-stalk and internally with the 

 colon as has been described above. 



Histolagy of the yolk-stalk, etc. (figs. 5, 6). — As seen in a trans- 

 verse section '*the yolk-stalk is nearly circular, with a fairly thick 

 wall bounding a spacious internal circular cavity. The thick wall 

 (fig. 6) is formed of : — 



(i) A single layer of very flat epithelial cells of epiblastic 

 origin. 



(ii) A fairly thick mesoblastic portion, many-layered and with 

 a large number of blood vessels, — both arteries and veins, arranged 

 near the inner periphery in a circle ; all the blood vessels are full 

 of blood corpuscles. The cells forming this portion are more or 

 less polygonal with slightly wavy walls and with a small nucleus. 



(iii) The innermost hypoblastic layer consisting of a single 

 layer of flat epithelial cells. 



The wall of the yolk-sac is also formed of the same three 

 layers, but the mesoblastic portion is not so thick and the hypo- 

 blastic layer is indistinguishable in some places. 



The blood vessels as ascertained by dissection and serial 

 sections were found to unite with one another, the arteries with 

 arteries and the veins with veins, until, near the point where 

 the yolk-stalk enters the body of the embryo, only a single large 

 artery and a single vein are to be seen. The connections of these 

 blood vessels with those of the embryo are as follows : the artery 

 opens into the dorsal aorta and the vein joins the hepatic portal 

 vein. The exact arrangement of the finer blood vessels on the 

 yolk-sac could not be followed. 



The contents of the yolk-sac and the stalk were minute, 

 nearl}^ circular yolk granules. 



The arrangement of the blood vessels and the connections 

 of the yolk-sac point to a double mode of absorption of its 

 contents, viz. (i) the direct transference of the yolk granules into 

 the colon through the yolk-stalk, and (ii) through the blood vessels. 



The above description is based on specimens obtained by dis- 

 section from two female specimens trawled at the south end of 

 Periya Paar on the coast of Ceylon, on 23rd of February, 1911, 

 There are nine well preserved specimens, besides some in poor condi- 

 tion. The two young shark-like embryos were also obtained from 

 the same locality on the 8th of December, 1910. The disc of the 

 parent fish measured about 2 feet 10 inches in breadth and there 

 was -a single embryo in each oviduct. 



Trygon kuhlii (Miiller and Henle). 

 (PI. XIX, fig. I.) 



1909. Trygon kuhlii, .\nnandale, of), cit,, pp. 34, 35. 



As shown in fig. i the outline of the disc of the single female 

 embryo before us is a quite regular curve, not at all angulate. 



