10. Observations on the Intra-uterine Embryos of 
Elasmobranchs. 
By T. Sournwett, A.R.C.S., F.Z.S., Director of Fisheries, Ben- 
gal-and Bihar and Orissa; and B. Praswap, DSc. 
A study of the intra-uterine embryos of Indian Elasmo- 
branch fishes has resulted in the elucidation of some very 
interesting problems, and in this paper we propose giving a 
general account of this work.! 
As is well known, both oviparous and viviparous forms are 
present amongst the Elasmobranchs, and the origin of vivipar- 
ous from the oviparous forms is a matter of very great zoologi- 
cal interest. Fortunately there exist among the living Elasmo- 
branchs almost all grades in the evolution of these forms, and 
by a study of these one is able to conjecture as to the prob- 
able line along which such evolution has taken place. The 
embryos in the course of the intra-uterine period of their exis- 
tence develop special structures which adapt them for the ab- 
sorption of food material from the maternal uterine tissues ; 
further they pass through a number of different stages which 
seem to be of the nature of recapitulatory stages and possibly 
represent the phylogenitic changes that have taken place in 
the history of the group. ; F 
In the oviparous Selachii like Scyllium and Raia there is 
no connection whatsoever between the mother and the embryo. 
tissue by the transformation of the yolk-sac into a placenta. 
As an example of this class may be cited the common Indian 
Bae rem er ne cnc re ee ne ea amreeaa aie 
} For anatomical and other details and literature refer to Rec. Ind. 
Mus,, XIX, pp. 215-241 (1919). 
