310 HYDRIDES. 



nodules; they are admirable instruments both for the 

 capture and destruction of prey. Worms and larvae, 

 Entomostraca, and even minute fishes constitute the food 

 of the Hydra and these are seized by the long, flexible 

 arms, and probably paralyzed by the threads which are 

 darted forth from the numerous batteries of thread-cells 

 covering their surface. It has been noticed that worms 

 which have escaped from the Hydra's grasp usually die 

 soon after, as if from the effects of some poisonous secre- 

 tion. 



The Hydra, which is little more than a locomotive 

 stomach and feeding- apparatus, is remarkable for its 

 voracity and activity in capturing prey, seizing a worm 

 " with as much eagerness as a cat catches a mouse"*. 



Like the rest of its tribe it is propagated in two ways, 

 by gemmation and by a true sexual reproduction. In 

 the earlier part of the year budding goes on rapidly, and 

 large numbers of young pullulate from various parts of the 

 body, which are developed into perfect polypites and 

 finally become detached. This vegetative process is 

 extremely productive : buds are often present on the 

 young Hydra before detachment; and as many as four 

 generations are sometimes organically united, so as to 

 form a composite being. " We have thus in a transient 

 stage of the life-history of the Hydra a representation of 

 that which is the permanent condition of most of the 

 hydroid zoophytes." Rarely, fissiparous reproduction 

 occurs, the fission being either longitudinal or transverse. 



At certain seasons, and especially towards autumn, 

 true reproductive organs are developed, the spermary and 

 ovary being usually present on the same individual, but 

 borne on different regions of the body. The ovary is 

 a simple sac, formed by a bulging of the body-wall ; and 



* Bkpr. 



