EMBRYOLOGY OF THE SEA LAMPREY 

 Table 9. — Living and dead embryos per sample and their stage of development at 62.5° F. {n^" C) 



135 



Sample 



28. 

 29. 

 30. 

 31. 

 32 

 33. 

 34. 

 35. 

 36 

 37. 

 38. 

 39. 

 40. 

 41. 

 42. 

 43. 

 44. 

 45 

 46 

 47, 

 48, 

 49, 

 50, 

 51, 

 52, 

 53 



Hours 



136 

 148 

 160 

 172 

 814 

 196 

 281 

 230 

 242 

 254 

 269 

 293 

 302 

 327 

 338 

 349 

 362 

 375 

 386 

 419 

 447 

 470 

 494 

 518 

 543 

 570 



Number 

 dead 



142 

 37 

 33 

 58 



57 

 76 

 44 

 70 

 65 

 86 

 40 

 75 

 78 

 53 

 64 

 96 

 85 

 96 



117 

 44 

 83 

 98 

 68 

 79 

 92 



Stace of living embryos 



Table 10. — Mortalities of sea lamprey eggs reared at a 

 constant temperature of 52.5° F. {11.4° C.) 



"dead" in the records for that sample (tables 11 

 and 12; fig. 27). The incidence of dead embryos 

 in the samples increased rather consistently as 

 development proceeded and was high in tlic later 

 stages. 



Overlapping was prominent between later stages 

 since individual stages lasted from 4 to 16 days 

 (table 6; fig. 28). Stage 13, the highest stage 

 reached, had lasted 384 hours (16 days) wlien the 

 experiment was finally terminated at 874 liours 

 (ca. 37 (hiys). Stages 12 and 13 overlapped 

 36 hours. 



A most interesting feature of this experiment 

 was the condition of embryos that finally reached 

 and remained in stage 13. Although they were in 

 stage 13, they were developing witliin the fertiliza- 

 tion membrane (chorion). The spirally curled 

 embryos developed transparent pericardia, pig- 

 ment spots, and hemoglobin which had a muddy 

 red to brown appearance in contrast to the normal 

 bright pink to red. Some of these embryos finally 

 were released wlien tlicir membranes disintegrated. 

 After release, however, the embryos did not 

 straighten out or develop further but remained 

 in this condition until death. 



During tliis test several abnormalities were 

 noted in the embryos: enlarged pericardia; straight 

 tubular hearts; shorter but heavier bodies; en- 

 larged gut region; a separation of yolk cells from 

 the gut walls; and failure to straighten from the 

 spirally curled position after removal of the 

 chorion. 



Development at 60° F. 



Tlie rate of dcveloiimcnt was much more rapid 

 and the overlap of stages was less at 60° F. than 

 at lower temperatures (tables 6, 13, and 14; fig. 

 28). The temperature of 60° F. was the lowest 

 at which viabU\ burrowing prolarvae (stage 17) 

 were produced. Mortality was generally less than 

 on corresponding (hiys in experiments at lower 

 temperatures (fig. 27) and abnormalities were 

 relativelv few. 



