CCELENTERATA : HYDROZOA. 91 



the mouth of the nectosac round its entire margin, and leaving 

 a central aperture. The peduncle by which the nectocalyx is 

 attached to the hydrosoma conveys a canal from the somatic 

 cavity, which dilates into a ciliated chamber, and gives off at 

 least four radiating canals, which proceed to the circumference 

 of the bell, where they are united by a circular vessel ; the 

 entire system constituting what is known as the system of the 

 " nectocalycine canals." In the typical Calycophorida two 

 nectocalyces only are present, but in some genera there are 

 more. In Pray a the two nectocalyces are so apposed to one 

 another that a sort of canal is formed by the union of two 

 grooves, one of which exists on the side of each nectocalyx. 

 This chamber, which is present in a more or less complete 

 form in all the genera, is termed the " hydrcecium," and the 

 ccenosarc can be retracted within it for protection. 



The reproductive bodies in the Calycophorida are in the 

 form of medusiform gonophores, which are budded from the 

 peduncles of the polypites, becoming, in many instances, de- 

 tached to lead an independent existence. In some Calycopho- 

 rufa, as in Abyla, " each segment of the ccenosarc, provided 

 with a polypite, its tentacle, reproductive organ, and hydro- 

 phyllium, as it acquires a certain size, becomes detached, and 

 leads an independent life the calyx of its reproductive organ 

 serving it as a propulsive apparatus. In this condition it may 

 acquire two or three times the dimensions it had when de- 

 tached, and some of its parts may become wonderfully altered 

 in form." (Huxley.) To these detached reproductive por- 

 tions of adult Calycophoridce the term " Diphyozooids" has 

 been applied. 



As regards the development of the Calycophoridce, "not only 

 the new polypites, but the new nectocalyces and reproductive 

 organs, and even the branches of the tentacles, are developed 

 on the proximal side of the old ones ; so that the distal ap- 

 pendages are the oldest." (Huxley.) The process of develop- 

 ment is, therefore, the reverse of what obtains amongst the 

 Hydroida. 



Diphyes, which may be taken as the type of the Calycophorida, 

 consists of a delicate filiform ccenosarc, provided proximally 

 with two large mitre-shaped nectocalyces, of which one lies 

 entirely on the distal side of the other. The pointed apex of 

 the distal nectocalyx is received into a special cavity in the 

 proximal nectocalyx. The "hydrcecium" is formed partially 

 by this charrfber in the nectocalyx, and partially by an arched 

 groove prolonged upon the inner surface of the distal necto- 

 calyx, within which the ccenosarc moves freely up and down, 



