98 PROCEEDINGS OF THE ACADEMY OF [1893. 



The membrane bones of the skull are already fairly well developed, 

 as are, in fact, the membrane bones throughout the body generally. 

 The vertebral rings of the vertebral column are already defined, 

 and are separated from each other by considerable inter-vertebral 

 spaces. Their dorsal and vertical outer margins are gently concave. 

 The ribs, the neural and hsemal arches are developed and the com- 

 plicated musculature of the caudal fin is already well marked. The 

 hypural pieces of the caudal are well-developed in cartilage and a 

 partly membranous matrix. The pectoral fins are already Avell- 

 developed but present as far as I have been able to make out no 

 such vascularization as the others. The ventrals are still small and 

 undeveloped. The lateral line system does not seem to be strongly 

 marked at this stage ; the small round pore behind the eye repre- 

 sents its connection with the exterior. The air bladder is devel- 

 oped and occupies considerable space at the point P in the body 

 cavity. Just in front of the air bladder is a large highly vascular 

 mass representing the Wolffian body or kidney. The glandular 

 portion of the Wolffian body is thus seen to be quite anterior in. 

 position. Cross-sections show that Wolffian ducts are present behind 

 the region of the Wolffian body as a pair of simple longitudinal 

 canals. These ducts pass backward parallel with each other as far 

 as the downward flexure of the hind gut H G. At this point they 

 suddenly bend downward and gradually converge so as to meet just 

 before opening to the exterior between the hernia-like protrusion of 

 the lower portion of the hind gut and the anterior margin of the 

 anal fin. 



As already stated the hind gut is very much enlarged in trans* 

 verse diameter, as may be seen from the accompanying figure. 

 Upon being cut open it is found to be filled up with villous or fila- 

 mentous productions of its lining mucous membrane. These villi 

 tend to be flattened, and with the widest portion of their bases 

 extending parallel with respect to each other and in conformity with 

 the length of the intestine. The anal opening A is found on the 

 posterior face of the hernia-like protrusion of the abdominal walL 

 caused by the hypertrophied hind-gut. The mid-gut is separated, 

 sharply from the hind-gut by a pyloric constriction just a little 

 below and behind P as shown in the diagram. The mid-gut or 

 gastric portion of the intestinal canal presents no very unusual fea- 

 tures except that its internal face is thrown into parallel longitudi- 



