134 



MANUAL OF ZOOLOGY. 



freely up and down, and can be entirely retracted if necessary. 

 The upper part of the ccenosarc dilates into a small ciliated 

 cavity, from which are given off two tubes, which proceed re- 

 spectively to the distal and proximal necto 1 

 calyces, where they open into the central 

 chamber from which the nectocalycine 

 canals take their rise. The upper portion 

 of this small ciliated cavity is prolonged 

 proximally into the larger chamber of the 

 " somatocyst." The ccenosarc (c) bears 

 polypites, each of which is protected by a 

 delicate glassy " hydrophyllium." 



ORDER II. PHYSOPHORID^E. This sec- 

 ond order of the Oceanic Hydrozoa com- 

 prises those Siphonophora in which the 

 hydrosoma consists of several polypites united 

 by a flexible, contractile, unb ranched or very 

 slightly branched ccenosarc, the proximal ex- 

 tremity of which is modified into a " pneuma- 

 tophore" and is sometimes provided with 

 " nectocalyces" The polypites have either a 

 . single basal* tentacle, or the. tentacles arise 

 directly from the connosarc. " Hydrophyllia " 

 are commonly present. The reproductive 

 bodies are developed upon gonoblastidia. 



The ccenosarc in the Physophoridce, like 

 that of the Calycophoridtz, is perfectly flex- 

 Fig. 55. Caiycophor- ible and contractile ; but it is not neces- 

 '1S*?$'$$3$. sarily elongated, being sometimes spheroidal 

 * v Proximal nectoca- or discoidal. The proximal end of the 



lyx : i/ Distal necto- j i i i 



. calyx-; k Hydrrecium ; ccenosarc " expands into a variously-shaped 

 ; c cce'nosarc, carrying enlargement, whose walls consist of both 



polypites each with its -1,1 11-1 



bract and tentacle. ectoderm and endoderm, and which en- 

 closes a wide cavity in free communica- 

 tion with that of the ccenosarc, and, like it, full of the nutritive 

 fluid. From the distal end, or apex, of this cavity depends 

 a sac, variously shaped, but always with tough, strong, and 

 elastic walls, composed of a substance which is stated to be 

 similar to chitine in composition, and more or less completely 

 filled with air" (Huxley). The large proximal dilatation of 

 the ccenosarc is termed the " pneumatophore," whilst the chiti- 

 nous air-sac which it contains is termed the " pneumatocyst " 

 (fig. 54, i). The pneumatocyst is held in position by the 

 reflection of the endoderm of the pneumatophore over it, and 

 it doubtless acts as a buoy or " float." In the Portuguese 



