422 



BULLETIN OF THE BUREAU OF FISHERIES. 



Figure 39 illustrates an egg shortly before hatching. The length of the embryo now 

 exceeds the circumference of the egg. The yolk mass is materially reduced and the em- 

 bryo moves freely within the egg membrane. Pigmentation has not increased materially 

 and the embryo remains relatively transparent. 



Larval development. — ^The incubation period, at laboratory temperature, occupies 

 six to seven days. The newly hatched lar\'se (fig. 40) are approximately 5 mm. in length. 



KntTLANDIA VAGRANS. 



Fig. 36. — Egg showing an early stage in differentia- 

 tion of embryo (e); EEA, extra-embryonic area of 

 embrj'onic shield. 



Fig. 37. — Egg showing later stage in differ- 

 entiatiou of embryo. 



The yolk sac is relatively small. The dorsal fin fold has its origin just posterior to the 

 head. Both dorsal and ventral fin folds are continuous. The depth of each fold does 

 not exceed half the depth of the body at the vent. The vent is located near the posterior 

 margin of the yolk sac. The newly hatched larvae are highly transparent. A few pig- 



KIRTLANDIA Vv\GR.\NS. 



Fig. 38. — Egg 40 hours after fertilization. 



Fig. 39. — Egg just before hatching. 



ment spots occur on the dorsal aspect of the head and in a Une at the base of the ventral 

 fin fold. 



Figure 41 illustrates a young fish 9 mm. in length. The body is relatively slender. 

 The soft dorsal and anal fins are becoming differentiated. A few pigment spots remain 

 scattered on the dorsal aspect of the head and a dark longitudinal line extends along the 

 side of the body. The silvery character of the side is not yet apparent. 



