REPRODUCTION OF HYDRACTINIA. 119 



On a first glance, we are apt to imagine that the 

 tentacula could be of little service to the polyp, for 

 even when they have fixed the errant prey, their 

 shortness must prevent them from conveying it to the 

 mouth. This is true ; but the difficulty is obviated 

 by the mobility of the head, which can not only be 

 shortened and lengthened at will, but can be turned 

 in any direction, so that its extremity may be applied 

 to whatever tentaculum the prey is adherent to. 



Colonies of these Hydractinise in a contracted state, 

 when first taken from the sea, resemble a gelatinous 

 crust investing the shell. They are liable to become 

 covered with a kind of mouldiness in still water; 

 whence it is probably a provision of nature to ensure 

 constant washing, that they frequent shells occupied 

 by so restless an animal as the Hermit Crab. 



The mode of reproduction in the Hydractinia re- 

 sembles in some respects that of the Tubularia above 

 described. Clusters of ovarian capsules are produced 

 immediately below the inferior row of tentacles (PL II. 

 fig. 3). These capsules are observable in all stages of 

 development, each being supported upon a very short 

 pedicle, and in their interior may be perceived one, 

 two, or even four embryonic corpuscles, each con- 

 tained in its own compartment : these, as they be- 

 come mature, escape into the surrounding water, at 

 which time they present the appearance of minute 

 Hydrse, and if placed in a watch-glass, these little 

 corpuscles soon become adherent thereunto, and gra- 

 dually assume the form of their parent. 



