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



folds, which, as shown in pi. xvii, fig. 3, become quite separated 

 here and there to form small fiat processes. These processes seem 

 to be the starting point for the formation of the more highly 

 evolved types of appendicula described further on. 



Type (ii). — In Scoliodon ivalheehmi the appendicula are of a 

 more advanced type. As seen with the naked eye the whole sur- 

 face of the placental cord is raised up into small tubular processes 

 (pi. xvii, fig. 4). The processes or appendicula measure 1*4 mm. 

 in length and "3 mm. to "5 mm. in breadth. The appendicula on 

 lieing examined with the microscope are seen to be small flattened 

 processes, broad at their free end and gradually narrowing to the 

 point of attachment. Some of them as shown in the figure (where 

 they are shown magnified 25 times) have notches anteriorly in posi- 

 tions where division might have taken place. With the low power 

 of the microscope the wall of the appendiculum, which is formed of 

 many layers of epithelial cells, appears of a much darker colour. 

 There is, however, in the appendicula of this type no vessel of any 

 kind such as that mentioned by Alcock {lac. cit.) for Z. hlochii. 

 Otherwise the appendicula of Z. blochii are very near those of this 

 type. 



Type (iii). — There are two embryos of a species of Scoliodon 

 before us from Madras preserved in situ in the uterus of one side. 

 The placenta in this species is of a type intermediate between the 

 simple one found in S. sorrakowah and the more highly evolved 

 arborescent one of 5. walheehmi. The placental cord, which 

 measures 72 mm. in length, is thickly covered with appendicula. 

 The appendicula as shown in pi. xvii, fig. 5 are elongated, much 

 branched structures ; the branches arise from a main axis and the 

 further branching is more or less dichotomous. The appendicula 

 are about 15 ram. in length, but not more than '25 mm. thick. Each 

 of the daughter branches is swollen at its extremity. No vessels 

 can be seen in preparations of this type of appendicula. 



Type (iv). — In S. sorrakowah and 5. palasorrah the appendi- 

 cula are elongated threads, simple or forked at a distance from the 

 point of origin (pi. xvii, fig. 6) ; they measure up to 60 mm. 

 in length. The appendicula in these two species have the same 

 structures as in the other three types, except that there is a blood 

 vessel in each. The placenta in the forms with this type of 

 appendicula is the least highly evolved, being a true yolk-sac 

 placenta, formed by the processes jutting out from the surface of 

 the yolk-sac and embedding themselves in the uterine wall 



It will be clear from what has been stated, that we can trace 

 a nearly complete series in the evolution of long thread-like single 

 or branching appendicula from mere projections on the wall 

 of the placental cord. It may also be noted here that the appen- 

 dicula may be present or absent in nearly related species of the 

 same genus ; for example, though they were described by Alcock 

 [loc. cit.) for Cestracion hlochii, they are absent on the placental 

 cord of a foetus of another species of Cestracion, from the collec- 

 tions of the ' Golden Crown' from the Bay of Bengal. It should 



