9* 



T. NISHIKAWA. 



across. All the fins are clearly visible, and the nasal sacs are to be seen as 

 two small pits. There are seven pairs of visceral clefts opening to the exterior, 

 of which the second is widest and the hindmost smallest. The first cleft has 

 now commenced to be metamorphosed into the spiracle. The upper jaw is still 

 in the form of a transverse ridge, and its two halves are still widely separated 

 in the median line. The external gills have begun to appear on each visceral 

 arch, including the spiracle ; and those of the second slit, or the first gill cleft of 

 the adult are longest. 



The head of this embryo is very different from that of the adult. In the 

 dorsal or ventral aspect the snout is pointed, but in profie it is rounded ; and 

 there is a small depression between the fore and mid-brain (fig. 3), so that the 

 head is already more or less compressed dorso-ventrally. In the dorsal view the 

 dueti endolymphatic! can be seen at the level of the first gill arch (fig. 6), and 



A 



