34 



HYDROZOA. 



to Huxley and Kolliker, is the structure of the 

 tentacular branches in Forskalia, and which 

 under slight modifications, repeats itself in many 

 other forms of Physophoridce and Calycophorich. 

 Within the sacculus of the last-mentioned order 

 occurs a peculiar zig-zag muscular cord, known as 

 the " angel-band," the nature of which is but im- 

 perfectly known. 



Where the pedicle and sacculus unite, a solid 

 process of the ectoderm has been observed to 

 originate in some Physophoridce. From its in- 

 vesting the sacculus in the form of a hood, this 

 organ has received the name of c involucrum. 5 



The mode of action of the tentacles, as appen- 

 dages for prehension, has been sufficiently explained 

 in our account of the Hydra. 



The name of € nematophores ' has been given by 

 Mr. Busk to peculiar csecal processes, distinct from 

 the oral tentacles, which are found on the coeuosarc 

 of some Sertularidce. Like the rest of the coenosarc 

 these processes are invested with a stiff, horny, 

 layer, open at the distal end of the nematophore, 

 beneath which are embedded many large thread- 

 cells. The nematophores probably serve as organs 

 of offence. They are most numerous in the genus 

 Plumularia. 























5 



Hilt 



Hyd 



The tegumentary 



the, in general, ciliated, ectoderm, and the rich 

 supply of thread-cells to which this layer give 



rise. 



more 



[ > 



may 



mass. 



Medusidce 



in 







i 



