IIYDROZOA. 93 



each is elevated on a conspicuous stalk. An 

 intermediate condition is presented by the genus 

 Haleclum, the polypites of which are 'sub-ses- 

 sile,' each hydrotheca being jointed to a short 

 procef!s of the coenosarc {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 ; shght 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,' witliin which numbers of thread-cells 

 are lodged. The tentacles are filiform, tapering 

 gradually towards their free extremities. In 

 Camjpanidina a delicate web-like extension from 

 the body of the polypite unites these appendages 

 for about a sixth of their entire length. 



Allusion has elsewhere been made to the nema- 

 tophores, or characteristic organs of offence, noticed 

 by ^Ir. Eusk in the genus Plumulai^ia, and one 

 or two of its immediate allies. These singular 

 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- 

 mularia have been observed to sting wdth some 

 severity. In Plumularia proper one of these 

 organs arises on either side of each hydrotheca, 

 while in Halicornaria they are situated, between 

 the pol3^pites, on the general surface of the 

 coenosarc. 



The reproductive organs vary, perhaps, less 

 than those of the Corynida\ and are usually sup- 



