1893.] NATURAL SCIENCES OF PHILADELPHIA. 9& 



nal folds, which curve in the direction of the flexure of this part of 

 the intestine which appears to form a loop upon itself. 



The function of the inter-radial and marginal plexuses of capilla- 

 ries of the young of these fishes, as the accompanying figure shows 

 must be in large measure respiratory. The figure shows the maxi- 

 mum proportional development of the vertical fins, but at a stage 

 about twice the length of the one here figured, the vertical fins 

 begin to become reduced in size so as to approximate their rela- 

 tively reduced proportions in the adult. The integuments of the 

 sides of the body now also become highly vascular, which dermal 

 vascularity also seems to disappear before the birth of the young. 

 The great vascular trunks that especially supply the vertical fins 

 with blood, as shown in the figure, also now atrophy in a measure 

 and become subservient only to the nourishment and metabolism of 

 the tissues of the fins. The histological changes in the fins of these 

 young viviparously developed fishes are therefore very great in the 

 course of their sojourn in the ovary of the parent. That the highly 

 vascular fins and the great vascular trunks which supply them, 

 must in a measure subserve a function in such foetal fishes very sim- 

 ilar to that of a placenta in a non-deciduate foetal mammal, there 

 can scarcely be any doubt. 



