58 HALF-HOURS IN THE GREEN LANES 



this ovum that a new hydra will be evolved in the 

 following spring. The first stage in the development 

 of a new hydra, from an egg, is very curions. When 

 first observed they are mere minute rounded lumps 

 of jelly, with starlike tenacles. When more ad- 

 vanced, the rounded part is lengthened into a small 

 foot-stalk (Fig. 52). The latter is still further 

 lengthened, and now the individual is supposed to 

 have arrived at a state of maturity. 



Mr. Fullagar found he could multiply the hydras 

 in his aquarium by cutting them up into slips as he 

 would plants ! So little did they seem to suffer by 

 this process that when the upper surface of an 

 individual was cut away from the stalk, the tentacles 

 immediately seized on a water-flea that happened to 

 come incautiously within their reach (Fig. 53). 

 Much more complex though the latter creatures are 

 than the hydra, when the tentacles close over them 

 and the water-flea is absorbed, it has to give up the 

 ghost, and submit to have its animal substances 

 digested. The little green hydra (H. viridis), also 

 to be met with, although not always so commonly, in 

 the same places as the vulgaris, does not appear to 

 differ in its habits or general organization. Both 

 species seem to have the power of benumbing or 

 paralysing the living objects that come in contact 

 with their tentacles, in a similar manner to that 

 possessed by sea-anemones. Mr. Fullagar discovered 

 that this stinging power was due to the presence of 

 certain fine threads contained in the numerous 



