HTDROZOA. " 93 



each is elevated on a conspicuous stalk. An 

 intermediate condition is presented by the genus 

 Haleciuim, the polypites of which are * sub-ses- 

 sile,' each hydrotheca being jointed to a short 

 procei?s of the cosnosarc (^fig. 1 8, c). 



The tentacles, though apparently disposed. 

 Hydra-like, in a single row below the mouth, are 

 found, on close examination, to exhibit an indis- 

 tinct alternate arrangement; slight differences in 

 length and position distinguishing those of the 

 two series. The peculiar rough appearance which 

 each tentacle presents resolves itself under the 

 microscope, into rows of minute elevations, or 

 ' palpocils,' within which numbers of thread-cells 

 are lodged. The tentacles are filiform, tapering 

 gradually towards their free extremities. In 

 Campanulina a delicate web-like extension from 

 the body of the polypite unites these appendages 

 for about a sixth of their entire lensfth. 



Allusion has elsewhere been made to the nema- 

 tophores, or characteristic organs of offence, noticed 

 by Mr. Busk in the genus Plmnulariaf and one 

 or two of its immediate allies. These sinsfular 

 appendages are well deserving of minute investi- 

 gation. Their offensive nature seems proved by 

 the abundance of thread-cells in their interior, 

 coupled with the fact that certain species of Plu- 

 niidaria have been observed to stinsr with some 

 severity. In Plumularia proper one of these 

 organs arises on either side of each hydrotheca, 

 while in Halicornaria they are situated, between 

 the polypites, on the general surface of the 

 coenosarc. 



The reproductive organs vary, perhaps, less 

 than those of the Corynidcc, and are usually sup- 



