GENERATION. 125 



of the last is unknown. Two kinds of medusa buds also 

 spring from the stock. The first of these (swimming bells) 

 are asexual. They remain attached to and move the stock 

 by the contractility of their walls. In the second kind, more 

 numerous than the preceding, the bells are of smaller size, 

 remain attached to stock, and at breeding seasons develop 

 sexual organs. Male and female elements contained in sep- 

 arate capsules. The impregnated egg gives birth to planulee 

 as before. 



In Cordylophora the planula is ciliated and of an oval form. 

 It soon becomes fixed, and develops through the winter a 

 fixed hydroid stock. From this numerous hydrse arise by 

 gemmation, each consisting of an elongated conoidal form 

 surmounted by tentacles. The following spring, two forms 

 of calyces are seen, one for the development of ova, the other 

 for spermatozoa. Impregnation occurring after a method 

 imperfectly understood, the contents of the ovisac undergo 

 segmentation, and a number of planulse escape, each of these 

 in turn to become fixed and develop the stock as before. 

 (Allman.) 



Ehizogeton resembles Cordylophora in having hydrse and 

 male and female calyces developed from hydroid stock. But 

 is peculiar in the stock not being shrub-like, but trailing; 

 each hydra and generative capsule (calyx) arises by its own 

 trunk. It appears probable that the calyces may be pro- 

 duced from hydree. The method of development of ova is 

 not known. (Clark.) 



In Eucope the form of the planulse and the stock are the 

 same as in Cordylophora. But when the special gemmse are 

 developed, but one form of calyx is seen, namely: that for 

 the development of the Medusae. Each capsule contains 

 about twenty to thirty buds, which, becoming detached, es- 

 cape and develop organs of generation, to bring forth in 

 their turn planulse. 



In Perigonimus no calyces are seen, the medusa buds spring- 

 ing directly from the sides of the stock, subsequently to 

 become detached. 



In Tubularia the hydraa are covered in by an extension of 



