EMBRYOLOGY OF THE SEA LAMPREY 



139 



Table 18. — Mortalities of sea lamprey eggs reared at a 

 constant temperature of 70° F. (21.1° C.) 



[Xo sample on 24th day] 



1 Terminal sample. 



The percentage of dead embryos in the samples 

 rose rapidly to 80 percent on the fourth day and 

 continued above 70 percent through the seventh 

 day after which hatching made the further samples 

 undependable as measured at mortality (table 18; 

 fig. 27). The percentage of embryos dead in the 

 70°-terminal sample (95 percent) indicates final 

 production a little less than half that at 60° F. 

 (88 percent dead in 60° terminal sample). 



Abnormalities in this experiment were relatively 

 few (15 to 20 percent of the prolarvae), but more 

 numerous than at 65° F. The abnormalities were 

 similar to those listed for the 60° F. test, especially 

 with respect to body shape. 



Development at 75° F. 



No viable, burrowing larvae were produced at a 

 constant temperature of 75° F. Heavy mortality 

 appeared early and persisted throughout develop- 

 ment (tables 19 and 20; fig. 27) with the result 

 that few embryos survived even to hatching. 

 With the exception of stages 2 and 3 the various 



Table 19. — Living and dead embryos per sample and their stage of development at 75° F. (23.9° C.) 



