HELEN D. PARK 



365 



an individual Hydra contributes to the curve. Howe\er, we now 

 have records of some 40 to 50 individual, isolated Hydra for peri- 

 ods of 80-240 days (Cf. 7). Hydra bearing spermaries were select- 

 ed from the stock cultures. Each Hydra was placed in 10 ml. of 

 BVT in a 30 ml. beaker and maintained as described above ex- 

 cept that buds were removed within 24 hours after separating from 

 the parents. 



Figure 2 shows the alternating sexual and asexual periods of 10 

 individuals left in their beakers throughout the observation per- 

 iod. Hydra #1, #4, and #5, whose records do not run 200 days, 

 were discarded because they began to grow small and became trans- 

 parent even though they appeared in ingest food and were pro- 

 ducing buds. As can be seen, 6-10 days after isolation, each 

 Hydra lost its spermaries. In the next 4-23 days each again diflFer- 

 entiated sexually. This sexual period was followed by alternating 



HYDRA: 



60 80 100 120 



DAYS AFTER ISOLATION 



200 



Fig. 2. Alternating sexual and asexual periods of 10 isolated, individual 

 Loomis stock Hydra observed for 200 days. Hydra 1, 4 and 5 discarded be- 

 cause of unhealthy appearance. Solid sections of bars, sexual periods; 

 hatched sections, asexual periods. 



