lS2 



MORRILL. 



[Vol. XI. 



of articulation with the metapterygial bone. The ventral rod 

 has a flattened conical enlargement on its posterior border for 

 the insertion of the muscles which move the ray. This projec- 

 tion has a height more than twice as great as the diameter of 

 the rod. The halves of the skeleton of the ray approach each 

 other distally. Their inner surfaces are quite firmly bound to- 

 gether by dense connective tissue. Each rod is nearly round 

 in section near its base, but becomes considerably flattened 

 dorso-ventrally in its distal half. The connective tissue in the 

 free rays is very abundant and dense. 



Muscles and Blood Supply. 



Three pairs of quite large muscles control the movements of 

 each free ray. 



The similarity of the musculature to that described in Trigla 

 makes it unnecessary to give a detailed description at this 

 time. 



The general arrangement of the blood vessels in the free 

 rays will be indicated in describing the cross section. 



Development. 



In a young sea-robin, probably P. evolans, lo mm. in length, 

 the anterior rays were as yet not in any way distinguished from 

 the others, since their separation from the fin had not begun, 

 being still united to them by the web of the fin. During the 



first day after its capture this fish increased 2 mm. in length, 

 and the membrane connecting the three anterior rays had 

 begun to disappear (Fig. i). The separation began by the 



