366 THE BIOLOGY OF HYDRA : 1961 



asexual and sexual periods varying greatly in length. Since my ar- 

 rival here, Dr. Robert Bryden has called my attention to Ito's ( 2 ) ob- 

 servation of such alternating sexual periods in Hydra magnipapilata. 



A striking characteristic of our isolated Hydra was the extreme 

 variability in duration of sexual periods for a given Hydra and 

 from Hydra to Hydra. For example, Hydra #6 went through 10 

 cycles while Hydra #2 went through only 3. Hydra #2 holds a rec- 

 ord in our laboratory for sustained production of spermaries— 103 

 days. I mention this in view of Brien's (1) statement that main- 

 tained sexuality results in death. 



I would like, before we leave these isolated Hydra, to give you 

 a bit of information which is not relevant to the main theme of this 

 paper, but which I obtained in order to answer a recurring ques- 

 tion, "Does sexuality have any effect on l^udding rate?" We now 

 have an answer for 22 of these isolated Hydra involving a total of 

 69 sexual and 75 asexual periods after the initial sexual period. The 

 budding rate per Hydra per day while sexual was 0.64 ± .08 and 

 the rate while asexual was 0.78 ± .10. The difference is not statisti- 

 cally significant, and we conclude that sexuality does not affect 

 budding rate. 



We have known since we established our mass cultures that they 

 are not sterile. We know that there are at least three kinds of pro- 

 tozoa, at least five kinds of bacteria; there are some molds. We have 

 not attempted sterile techniques. Some time ago I was quite im- 

 pressed by the possibility that the rhythmic nature of sexual dif- 

 ferentiation might be related to a rhythm in some other organism 

 or organisms in the cultures. We thought, therefore, that we would 

 see if keeping individual, isolated Hydra "cleaner" would have 

 any effect on the duration of sexual periods. Accordingly, we left 

 half of the individuals in the same beakers for 100 days and changed 

 the other half to clean beakers daily except Sunday. Other pro- 

 cedures were the same as those described above. 



Figure 3 shows the results of two replicate experiments. Again, 

 we found great variation in the lengths of sexual periods for a given 

 Hydra and from Hydra to Hydra. The mean number of sexual 

 days per Hydra in the changed group was 44 ±12 and in the un- 

 changed group, 50 ± 13. The difference is not statistically significant 

 and indicates that the rhythm of sexual differentiation was not 



