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



the circulation of blood. We have been able to distinguish three 

 distinct grades in the development of the placenta in these 

 forms : — 



(i) In S. sorrakotvah and 5. palasorrah we have the least modi- 

 fied type of placenta. As shown in pi. xvii, fig. 10, it is the 

 original yolk-sac of the typical rounded to slightly ovoid form. 

 At its lower free extremity it has a number of small protuber^ 

 ances which, as seen in pi. xvii, fig. c,, are embedded in the 

 maternal uterine tissue and form a very simple type of yolk-sac 

 placenta. 



(ii) A placenta of a slightly more advanced type is the one 

 mentioned by Miiller, op. cit., in his description of the placenta of 

 Mustelus laevis and a species of Carcharias, where there is a distinct 

 placenta-like interdigitation of folds of the yolk-sac, and these 

 villi-like projections fit into corresponding depressions in the 

 uterine mucous membrane of the mother like the cotyledons of the 

 ruminant placenta. 



(iii) In a specimen of Scoliodon sp. from Cejdon the yolk-sac 

 has practically disappeared as such, and in its place we find that 

 the placental cord broadens out into a flattened structure showing 

 traces of division and transformation into an arborescent mass. 

 The placenta in the two specimens of Scoliodon from Madras is still 

 simpler than this, and is of a character intermediate between that 

 of the second type and the one found in Scoliodon from Ceylon. 

 This type when fully evolved is a fairly large arborescent structure 

 formed by the continued subdivision of the distal extremity of 

 the placental cord and the remains of the yolk-sac. The blood 

 vessels in the placental cord also divide again and again to supply 

 the various subdivisions of the placenta, which is a highly 

 vascular structure. The placenta is in close connection with a flat 

 highly vascular portion of the maternal uterine wall. Each embryo 

 is connected by a separate placental connection with a separate 

 part of the uterine wall. This type is found in Scoliodon walheehmi 

 (pi. xvii, fig. I, shows a side view of only the foetal placental por- 

 tion with the embryo and the placental cord), and has been shown 

 by Alcock to occur in Carcharias rnelanopterus, Cesiracion hlochii 

 and Carcharias dussumieri. 



Branchial Filaments. 



In the earlier stages of the intra-uterine embryos of many 

 Batoids large numbers of delicate and much elongated branchial 

 filaments protruding out of the branchial openings of the embryos 

 have been described by many authors. In the course of our 

 studies we also have found these to be present in a number of 

 species from which they had not been recorded previously. These 

 filaments are the greatly elongated gill-processes which issue out 

 of all the branchial slits ventrally except for the spiracles, and are 

 so numerous as to form about one-third of the whole volume 



