XX INTRODUCTION. 



enabling the zoophyte to seize food scattered about on tin- 

 ground by the Crab when feeding*. 



Perhaps the most extraordinary of the crenosarcal ap- 

 pendages met with amongst the Hydroida are the snake- 

 like organs with which the genus Ojthiodes is furnished. 

 (Plate XLV. fig. 2 a.) One of them is always stationed 

 close to the polypite, and great numbers are distributed 

 upon the creeping stolon. They are vigorous in their 

 movements, capable of enormous elongation, and sur- 

 mounted by a large capitulum, thickly covered with 

 thread- cells. They may act not only as organs of defence, 

 but also as auxiliaries in the capture of food. 



The Hydroid colony is enlarged by a purely vegetative 

 process : fresh polypites bud rapidly from the prolific pulp ; 

 and in the larger and arborescent kinds branches and 

 branchlets germinate, according to the pattern of the 

 species, from the zoophyte as from the tree. For the 

 multiplication and diffusion of the species, special zooids 

 are set apart; and to them is allotted the reproductive 

 function, as to the polypite that of nutrition. They cor- 

 respond with the flower-buds of the plant. 



REPRODUCTION. 



The polypites, or feeders, of the Hydroid colony are 

 almost always present ; the sexual zooids are developed at 

 certain seasons only, in buds of peculiar structure, which 

 occupy different positions in different species. Amongst 



* Allman regards these filaments " as an abnormal state of the ordinary 

 polypite," and stales that they are not usually present. But on examination 

 Iliey are found to bear the cln.-rM resemblance to a tentacle, bring slightly 

 enlarged towards the tip, and endowed with extraordinary extensibility. 

 They oeeiir both on Hydractinia and Podocoryne cnrnca, and, I believe, are 

 very generally present, though when contracted they are with difficulty 

 recogni/.i '' 



