1893.] 



NATURAL SCIENCES OF PHILADELPHIA. 



95 



THE VASCULAR RESPIRATORY MECHANISM OF THE VERTICAL FINS 

 OF THE VIVIPAROUS EMBIOTOCIDJE. 



BY JOHN A. RYDER. 



The young surf-perch, Ditrema laterale, from which this figure is 

 drawn, measured about twenty-three millimetres in length. It was 

 one of several which were removed from the saccular ovary of 

 the parent, each young fish lying lengthwise and disposed so as to 

 bring the enormously expanded vertical fins into contact with the 

 wide ovarian folds and the sides of the ovarian walls. As can be 

 seen from the figure, the lateral area of the vertical fins quite equals, 



if it does not exceed, the lateral areas of the body. In fact, the 

 dorsal is as high as the body is deep. In the same way the caudal 

 fin is as wide at its widest part as the body's greatest width. The 

 total length of the caudal is not far from a third of the total length 

 of this larval stage. Another feature which distinguishes this 

 young fish from the young of all other species is the highly vascu- 

 lar condition of the inter-radial membranes of the vertical fins. 

 This vascularity is not only obvious when the object is viewed with 

 a transmitted light, but also in sections. The most marked devel- 

 opment of capillary vessels is found in the flattened lobes with 

 which the fins are bordered. Fourteen very distinct lobes with deep 

 notches between them are found along the margin of the tail ; about 



