EMBRYOLOGY OF THE SEA LAMPREY 



133 



Table 6. — Hours at which the first and last specimens of the various stages appeared in samples during each experiment 



and the duration of stages {in parentheses) 



' Termination of experiment. 



' 100-percent mortality subsequent to this hour. 



J No embryo of this stage found in any sample. 



' These blanks cannot be filled properly for these stages were sampled 

 either in or immediately preceding the terminal sample. 



65° 



TEMPERATURE (°F) 



FincRE 28. — Number of hours required by sea lamprey 

 embryos to reach different developmental stages when 

 reared at variou.s constant temperatures. 



of the eggs were dead. All eggs obviously were 

 dead in samples taken after the 5th day (table 

 5). Eggs marked by lesions as described by 

 Damas (1948) did not undergo first cleavage. 



The highest stage completed in this experiment 

 was stage 2, since stage 3 was not consummated. 



Development at 50° F. 



The rate of development was decidedly faster at 

 50° F. than at 45° F. (table 6; fig. 28) and devel- 

 opment proceeded farther. Stage 9 was reached 

 but few embryos survived to the end of the stage 

 (tables 7 and 8; fig. 27). A single sample con- 

 tained eggs that seemed to be intermediate between 

 stages 9 and 10. No embryos were alive after the 

 270 hours (sample 65, table 7; table 6, also fig. 27). 



The duration of each of the first 6 stages fell 

 within the limited range of 15-20 hours (table 6). 

 Stage 7, however, lasted 35 hours, and stage 8 

 approximately 65 hours, the longest save for tlie 

 last stage reached (stage 9). The greatest period 

 overlap of stages occurred between stages 7 and 8 



