138 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 

 Table 15. — Living and dead embryos per sample and their stage of development at 66° F. {18.4° C.) 



Table 16. — Mortalities of sea lamprey eggs reared at a 

 constant temperature of 65° F. (.18.4° C) 



' Terminal sample. 



among the experiments and represents unusually 

 good- results for the artificial rearing of fish eggs 

 of any kind. 



Abnormalities were extremely few, appi'oxi- 

 mately 2 to 5 percent, mostly in the last samples. 

 A few specimens had enlarged pericardia with a 

 straight, tubular heart, and several had yolk 

 separation and the associated hydrocoelus gut. 

 One "twin" embryo was seen. These twins, in 

 early stage 12, possessed a common but somewhat 

 enlarged blastopore (fig. 29). 



Development at 70° F. 



The rate of development at 70° F. was only 

 slightly accelerated over that at 65° F., in fact 



Figure 29. — Posterolateral view of twin embryo.s, showing 

 the common, but enlarged, blastopore. 



embryos reared at 70° F. reached stages 2 and 4 

 later than did those reared at 65° F. (table 6; 

 fig. 28), and the limited overlap of stages charac- 

 terized embryos at both temperatures. More 

 pronounced and more significant were the increase 

 of mortality (tables 17 and 18; fig. 27) and the 

 greater number of abnormalities at 70° F. as 

 compared with the "optimum" of 65° F. 



At 70° F. as in the 65° test, the overlapping of 

 stages was limited to a slight overlap between 

 stages 11 and 12 and a somewhat greater one 

 between stages 13 and 14 (tables 6 and 17). 

 Elsewhere, the progression from one stage into 

 the next was precise. Stage 8 was prolonged 

 over 11 samples covering 32 hours, as against 

 2 to 3 for all other early stages. 



