ABSTRACT 



Early embryology of the sea lamprey has been subdivided into 19 stages. The 

 stages are based largely on external morphology, behavior, and organ function. 

 The holoblastic cleavage of sea lamprey eggs exhibited tviro types of third and 

 fourth cleavages, equatorial and meridional. The open blastopore had an ap- 

 parent migration over the surface of the embryo until it became the anus. Gas- 

 trulation resembles teleostean gastrulation in some characteristics and amphibian 

 in others. Lamprey neurulation resembles teleostean neurulation more closely 

 than it does amphibian. 



Sea lamprey eggs were reared experimentally at 10 constant temperatures 

 (at 5° intervals from 45° to 80° F., inclusive, and at 52.5° and 77.5° F.). No 

 viable, burrowing larvae were produced at any temperature below 60° F. or above 

 70° F. Optimum temperature was 65° F. which yielded 78 percent survival to 

 the burrowing stage; survival to the same stage was much lower at 60° F. (12 

 percent) and 70° F. (5 percent). The stage attained before all embryos were dead 

 decreased as the temperatures were shifted in either direction from the 60°-70° F. 

 interval. In general, developmental rate became faster, lengths of stages became 

 shorter, and overlap between stages was lessened as temperature increased. 



The evidence that sea lamprey eggs can develop successfully only within a 

 limited temperature range suggests that unfavorable temperatures may account 

 for the failure of certain apparently suitable streams to produce larval lampreys. 



