EMBRYOLOGY OF THE SEA LAMPREY 

 Table 13. — Living and dead embryos per sample and their stage of development at 60° F. (16.6° C.) 



137 



Table 14. — Mortalities of sea lamprey eggs reared at a 

 constant temperature of 60° F. {16.5° C.) 



[Xo sample on 17th day] 



' Terminal sample. 



from a fiiihirc of the stomiulaoiiin to open. An 

 enormous enlargement or ballooning of the 

 pharyngeal region resulted, especially in the 

 anterior portion, which tended to compress the 

 branchial structures and cause them to become 

 malformed and from all indication, non-functional. 



A midline cleft in the dorsal lip was designated 

 a "cleft-lip" abnormality. 



Development at 65° F. 



The rearing of sea lamprey eggs under constant 

 temperature was more successful at 65° F. than 

 at any lower or higher level (tables 15 and 16; 

 fig. 27). Development was rapid (tables 6 and 

 15; fig. 28), overlapping of stages was practically 

 nil, mortality was low, and abnormalities were 

 few. The details offered in this section are 

 based on an experiment conducted under refrigera- 

 tion. Essentiall}' the same results were obtained 

 in experiments conducted with heat and the 

 circulator. 



Stages did not overlap at 65° F. with the 

 exception of the overlap of stages 4 and 5 and 

 of stages 13 and 14. 



The percentage of dead embryos was low in 

 most samples but the day-to-day variation of that 

 percentage (fig. 27) was highly erratic and for 

 several dn,ys the percentage exceeded that of the 

 terminal sample taken on the 19th day. No 

 verifiable explanation can be offered for tliis 

 behavior of the percentages, but it is possible that 

 dead eggs were not distributed evenly through 

 the experimental lot and that certain samples 

 happened to be taken from points at which dead 

 embryos were concentrated. The 78-percent sur- 

 vival to the end of tlie experiment (only 22 percent 

 dead in the terminal sample) was by far the highest 



