LARVAL TELE OS TS 



22$ 



varied and striking of all larval fishes, and, singularly 

 enough, appear to be crowded into the briefest space of 

 time ; the young fish, hatched often as early as on the 

 fourth day, is then of the most immature character ; it 

 is transparent, delicate, inactive, easily injured; within 

 a month, however, it may have assumed almost every 

 detail of its mature form. A form hatching three mille- 

 metres in length may acquire the adult form before it 

 becomes much longer than a centimetre. 



The larval life of the common Sea-bream, or Gunner, 

 Ctenolabnts ccerulcns, has been admirably figured by A. 

 Agassiz. The newly hatched fish (Fig. 303) has the yolk 

 sac appended at the throat, as a large, transparent, if 

 slightly tinted, globule ; save for its great delicacy and 

 transparency, it may generally be compared to the corre- 

 sponding larva of Acipenser (Fig. 296). By the third day 

 (Fig. 304), the yolk sac has become greatly reduced, the 

 trunk elongated, the fin fold less conspicuous ; primitive 

 segments have appeared ; the pectoral fin has arisen, but 

 is not of the elasmobranch form of the similar stage (Fig. 

 298) of sturgeon ; it is long, thin, transparent, and its 

 rapid growth indicates its metamorphosed character. The 

 mouth, S, is in this stage on the point of formation. In 

 a slightly older larva (Fig. 305), the yolk has almost dis- 

 appeared ; its gill slits, GS, and mouth have now been 

 formed, and with the latter the nasal apertures. In a fol- 

 lowing stage (Figs. 306, 307), a well-marked opercular fold 

 makes its appearance ; pectoral fins acquire their com- 

 pleted outline and the fin fold undergoes changes : ante- 

 riorly it acquires supporting actinotrichia, posteriorly the 

 dermal supports of the caudal fin appear and at their bases 

 the coalesced radio-basals ; a ganoidean heterocercy is 

 here apparent, its distal tip the membranous opisthure, O. 

 Q 



