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HYDROZOA. 93 



each is elevated on a conspicuous stalk. An 

 intermediate condition is presented by the genus 

 Halecium, the polypites of which are < sub-ses- 

 sile/ each hydrotheca being jointed to a short 

 process of the coenosarc {fig. 1 8, 6). 



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 



of the 



, length * — r to ™, wv , 



, 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 



1 I gradually towards their free extremities. In 



Campanulina a delicate web-like extension from 



aii: the body of the polypite unites these appendages 



for about a sixth of their entire length. 



Allusion has elsewhere been made to the nema- 



uct tophores, or characteristic organs of offence, noticed 



Mr 



d or two of its immediate allies. These singular 



appendages are well deserving of minute investi- 

 ng gation. Their offensive nature seems proved by 

 y the abundance of thread-cells in their interior, 

 ^ coupled with the fact that certain species of Phi- 



mularia have been observed to sting 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 Corynidce, and are usually sup- 



