I 12 



CHIM^EROID FISHES AND THEIR DEVELOPMENT. 



of the yolk-sac (plate x, fig. 5i b , ys); its form at this stage is probably modeled 

 somewhat differently from that of the latest stage of the encapsuled embryo; thus 

 the membranes of the unpaired fin in the tail region are probably less marked than 

 in the earlier stage (comparing the embryo of plate ix, fig. 50) in which this mem- 

 brane serves as an organ for carrying out the water used in the respiration of the 



go 



Fig. 90. Late stage of Chimrera affinis (>). 



The yolk-sac is largely resorbed. The present is the type specimen of Professor VailUnl, and i> preserved in the ichthyological museum of the Jardin 

 des Plantes, bearing the number 42392. In spite of its small size (its total length is only about 1 I cm.) it shows a well-developed mixipterygium 

 (B) . A detail showing the vascular supply of the yolk-sac is indicated at A. 

 Fig. 91. Detail of early Chimeera monstrosa, showing larval coloration. 



After sketch of specimen in the museum of Tromsoe. Colors are indicated, a, ashen, if, white. 

 Fig. 92. Detail of Chimsera monstrosa indicating final larval coloration. After sketch of specimen in the museum in Copenhagen. 



encapsuled young. The advancing characters of the earlier young may best be 

 followed by contrasting figs. 51, 52, and 53. The changes thus observed are: 



In proportions. The head length of the embryo, measured for example anterior 

 to the base of the dorsal fin, decreases as we ascend the scale ; in the earlier stage it 

 measures about 20 per cent, of the entire length, in the latest about 16 per cent. ; 

 the eye alters little in size, but the region of the head lying below the eye increases 

 notably; the shape of the pectoral fin changes progressively; almost as wide as high 

 in the first figure, it becomes nearly twice as high as wide in the latest stage. So, 



