COMPOSITE HYDROZOA — CORTNIDJE. 461 



spring, the parents not being able to survive the cold season ; 

 whilst the budding process naturally takes place only during .the 

 warmer part of the year, but may be made to continue through 

 the whole winter, by keeping the water inhabited by the polypes 

 at a sufficiently high temperature. The Hydra possesses the 

 power of free locomotion, being able to remove from the spot to 

 which it has attached itself, to any other that may be more suit- 

 able to its wants ; its changes of place, however, seem rather to 

 be performed under the influence of light, towards which the 

 Hydra seeks to move itself, than with reference to the search 

 after food. 



302. Some of the simpler forms of the composite Hydrozoa 

 may be likened to a Hydra, whose gemmse, instead of becoming 

 detached, remain permanently connected with the parent ; and 

 as these in their turn may develope gemmae from their own 

 bodies, a structure of more or less arborescent character may be 

 produced. The form which this will present, and the relation of 

 the component polypes to each other, will depend upon the mode 

 in which the gemmation takes place ; in all instances, however, 

 the entire cluster is produced by continuous growth from a single 

 individual ; and the stomachs of the several polypes are united 

 by tubes, which proceed from the base of each other, along the 

 stalk and branches, to communicate with the cavity of the cen- 

 tral stem. This is the case with the family Corynidce, which are 

 composite fabrics, sometimes quite arborescent in form, but 

 unpossessed of any firm investment, the external wall being only 

 strengthened by a thin horny cuticle. A very beautiful marine 

 species of this family (the Coryne pusilla), is common on sea- 

 weeds and stones between the tide-marks ; sometimes clustering 

 parasitically round the stalks of Tubularia so as to form a thick 

 beard-like mossiness; each aggregate structure, however, not 

 being more than an inch in length. The tentacula (as in Fig. 

 222, a) are short, and arise from the whole surface of the body of 

 the polype, instead of from the margin of the mouth alone ; and 

 at first it seems difficult to understand how they can be of ser- 

 vice in bringing food to the mouth, which is situated at the very 

 extremity of the branch. Observation of the living animal, 

 however, soon removes this difficulty ; for the head is so very 

 flexible, that the mouth can bend itself down towards any of the 

 tentacula which may have entrapped prey; all its movements are 

 performed, however, in a very leisurely manner. The fresh- 

 water genus Cordylophora has yet been only found in a few loca- 

 lities ; and the chief interest attaching to it is derived from the 

 fact of its having been made the subject of an admirable Memoir 

 by Prof. AUman,' to which every one should refer, who desires 

 to acquaint himself with the minute organization of this group 

 of Zoophytes. The phenomena of the Reproductive process 

 exhibited by these Hydrozoa, are extremely curious. In Coryne 



' " Philos. Transact." 1853. 



