

Microns 



20 



Figure 331. — Larva of C virginica at the time of its 

 emergence 6 to 6}^ hours after fertilization. Drawn 

 from a photomicrograph of a live larva. 



Hole laboratory at room temperatures varjdng 

 from 22. .5° to 24.5° C. and salinity of water of 

 32.2 °/oo are given in table 37. To obtain re- 

 cords of rates of development at different tem- 

 peratm-es, several hundred artificially fertilized 

 eggs were placed in each Syracuse dish filled with 

 fresh sea water and coveretl to prevent evaporation. 

 The debris was removed, and the water contained 

 no unfertilized or cytolyzed eggs. 



Table 37. — Observations on the time required for artificially 

 fertilized eggs of C. virginica to reach trochophore stage 



All observations were made at Woods Hole in July at room temperatures 

 varying from 23° to 25" C. Tlie time required to reach different stages 

 varied in different groups of eggs. Tlie observations are arranged in two 

 groups; A and B. wliich differ primarily in the duration of time required 

 to reach rotating blastula and trochopliore stages. 



STAGES 



Stage of development 



Fertilization membrane- 

 First polar body _.. 



Second polar body 



First cleavage 



Second cleavage 



Third cleavage 



Morula stage 



Rotating blastula 



Trochophore 



5 min 



40 min 



1 hr. 10 min. 

 1 hr. 12 min. 



2 hr. 10 min. 



4hr. 

 5hr. 



10 to 25 min. 

 25 to 62 min. 

 40 to 65 min. 

 45 min. 

 62 to 120 min. 

 55 to 195 min. 

 135 min. 

 fi hr. 30 min. 

 8 to9hr. 







Centimeters 



Figure 332. — The emergence of larvae of C. virginica from fertilized eggs? kept in a finger bowl. The free-swimming 

 larvae form columns, which tend to disper.se at the surface. Drawn from life. 



350 



FISH AND WILDLIFE SERVICE 



