168 



K. S. LASHLEY 



from a population in a very small stagnant pond in the neighbor- 

 hood of Baltimore. Very extensive seasonal changes are evident 

 from the mean of the population at different times. 



Numbers of tentacles less than 5 or greater than 9 probably 

 can not be considered normal for H. viridis from this neighborhood. 

 Buds formed with less than four tentacles are usually small and 

 do not extend their tentacles. They either produce more ten- 

 tacles quickly, or die. The only individuals with ten tentacles 

 which I have found were small-bodied, dark in color, and pro- 

 duced buds very slowly. In H. grisea a large number of ten- 

 tacles seems to present a rather unstable condition. Individuals 

 with more than eight tentacles in my cultures have shown a 

 tendency to divide lengthwise and thus reduce the number of 

 tentacles to the mode. I have observed longitudinal division 

 in only one specimen of H. viridis, which bore six tentacles at 

 the beginning of division and gave rise to two polyps, each with 

 six tentacles. 



As individual polyps grow older they form additional tentacles, 

 a condition first observed by Marshall ('82) in H. viridis. Hase 

 has demonstrated a like condition in H. fusca and Hanel in H. 

 grisea. Hanel has found that the addition of tentacles occurs 

 even in polyps which are starving, although hunger tends to 

 inhibit the process, as is clear from table 7. Parke found that 

 the number of tentacles might be reduced and Hanel' s table 

 shows that this reduction is favored bv starvation. Mv own 



TABLE 7 



Changes in the number of tentacles of 129 specimens of Hydra grisea during one 

 month'' s cultivation; after Hanel 



Number of tentacles added 



Number of polyps showing change 

 Number of tentacles absorbed. . . . 

 Number of polyps showing change 



Number of polyps unchanged 



Total number of polyps 



Mean increase per individual 



