CCELENTERATA : SIPHONOPHORA. 133 



already described ; but the former is devoid of the gastric or 

 genital sac the " manubrium " possessed by the latter. Each 

 nectocalyx consists of a bell-shaped cup, attached by its base 

 to the hydrosoma, and provided with a muscular lining in the 

 interior of its cavity, or "nectosac." There is also always a 

 " velum " or " veil," in the form of a membrane attached to 

 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 Calycophoridcz two 

 nectocalyces only are present, but in some genera there are 

 more. In Praya 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 Calycophoridcz are in the form of medusi- 

 form gonophores, which are budded from the peduncles of the polypites, 

 becoming, in many instances, detached to lead an independent existence. 

 In some Calycophoridcz^ as in Abyla, "each segment of the ccenosarc, pro- 

 vided with a polypite, its tentacle, reproductive organ, and hydrophyllium, 

 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 attached, and some of its parts may become wonderfully altered in 

 form" (Huxley). To these detached reproductive portions of adult Caly- 

 cophoridfz the term ' ' Diphyozooids " has been applied. 



As regards the development of the Calycophoridcz, "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 appendages are the oldest " (Huxley). The pro- 

 cess of development is therefore the reverse of what obtains amongst the 

 Hydroida. 



Diphyes (fig. 55), which may be taken as the type of the 

 Calycophoridtt) consists of a delicate filiform coenosarc, pro- 

 vided proximally with two large mitre- shaped nectocalyces 

 (7;, v'\ 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" 

 (h) is formed partially by this chamber in the nectocalyx, and 

 partially by an arched groove prolonged upon the inner surface 

 of the distal nectocalyx, within which the ccenosarc moves 



