OBSERVATIONS ON HYDRA 595 



a few minutes it stretches out and extends little projections 

 which develop into tentacles during the next twenty-four hours. 

 It is then able to feed. The rupture of the shell suggests the 

 formation of a hatching ferment, such as has been described 

 in Lepidosiren and Teleostean fishes (15). 



Abnormalities are not uncommon among newly hatched 

 Hydras, possibly due to injuries during hatching. Several 

 two-headed specimens appeared, the double part varying in 

 length. Such specimens are not infrequent among adult 

 Hydras. In one or two cases the division appears to be growing 

 gradually deeper, so that eventually the compound would split 



Text-fig. 1. 



into two separate Hydras, but in most cases the specimens 

 remained without change for weeks and died without further 

 division. In no case was there any suggestion that a process 

 of fusion was going on. In two specimens the hypostome only 

 was double and several of the tentacles belonged to both rings. 

 The origin of a double Hydra can sometimes be observed 

 (Text-fig. 1). One normal specimen produced two buds close 

 together (Text-fig. 1, a), and in the course of development 

 these grew out on a common stalk. Although one of the 

 buds was a day or two younger than the other, they soon grew 

 to equal size. This double individual then separated (Text- 

 fig. 1, h) from the normal parent, and a week later both of its 

 limbs produced normal buds which separated off. Two days 

 later a third bud was formed near the junction of the two 

 limbs (Text-fig. 1, c). The next day a curious pointed projection 

 grew up between the bud and one limb (Text -fig. 1, d). Even- 

 tually this grew into a second bud joined to the first (Text- 



R r 2 



