234 Records of the Indian Museum. [Vol,. XVI, 



Internal anatomy, — The only features worth noting are: — (i) 

 The very large colon with a well-developed spiral valve. The 

 colon measures 21 mm. in length ; on being slit open it was found 

 to be filled with yolk granules. Lying dorsal to and opening into 

 the colon is (ii) the large internal yolk-sac. It is connected with 

 the small external yolk-sac through the yolk-stalk. The stomach 

 was quite empty, (iii) The rectal gland is a large structure, 

 (iv) The liver is comparatively small. The specimen dissected was 

 a male and shows the male organs, but not fully developed. 

 Ivcydig's organ is not quite developed, the vas deferens is also small 

 and not so convoluted. 



Two specimens, a male and a female, were obtained from a 

 large fish trawled in Portugal Bay on the i6th of February, 1910. 



The Yoi,k-stalk and the Placental Cord. 



A few remarks about these structures will not be out of place 

 here. In the sharks, as will be shown further on, the placenta is 

 purely of the nature of a yolk-sac placenta, in some more highly 

 evolved than in others. The arrangement and relations of the 

 blood vessels in the yolk-stalk of the Batoids, e.g. in Rhinohatis 

 columnae, are of a type essentially similar to that of the sharks. 

 In the more highly advanced or evolved forms of placenta of 

 sharks such as Scoliodon walbeehmi , the channel of the yolk-sac is 

 obliterated in the later stages of development, owing to there 

 being no yolk to absorb and the channel in the yolk-stalk being 

 therefore unnecessary, and further owing to the blood vessels 

 having developed to a much greater extent. The yolk-stalk now 

 becomes the placental cord and instead of the channel in the 

 yolk-stalk there is now^ a large artery and a large vein. The 

 cavities of unknown function lying next to the blood vessels des- 

 cribed in the account of the structure of the placental cord of 

 Scoliodon walbeehmi may possibly be the remains of the original 

 channel. Another point worthy of note is that the connection 

 between the yolk-stalk and the intestine of the embryo must be 

 stopped before the transformation of the yolk-stalk into the 

 placental cord takes place. As in the earlier stages of the develop- 

 ment of the sharks there is a yolk-sac and a yolk-stalk, the stage 

 v,?here there is a direct communication between the yolk-sac and 

 the intestine must exist even in forms that later on have a placental 

 arrangement. Unfortunately we have no material of the very 

 young stages of these sharks at our disposal that would support 

 these theoretical conclusions. 



In their descriptions of the embryos, some authors have 

 designated the yolk- stalk of the aplacental Batoids the umbilical 

 cord. This apparently is a misnomer, as in view of what has been 

 stated above, though the yolk-stalk or the stalk of the yolk-sac is 

 transformed in the sharks into the placental cord on the develop- 

 ment of the placenta, the converse is never true. In the Batoids 

 with the condition of aplacental viviparity the yolk-stalk has 



