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MANUAL OF ZOOLOGY. 



end of the ccenosarc dilates a little, and becomes ciliated in. 

 ternally, forming a small chamber" which communicates with 

 the nectocalycine canals. " At its upper end this chamber is 

 a little constricted, and so passes, by a more or less narrowed 

 channel, into a variously-shaped sac, whose walls are directly 

 continuous with its own, and which will henceforward be termed 

 the somatocyst (fig. i8, 3 b). The endoderm of this sac is cil- 

 iated, and it is generally so immensely vacuolated as almost to 



Fig. 18. — Morphology of the Oceanic Hydrozoa. i. Diagr.im of the proximal ex- 

 tremity of a Physophorid. a Pneumatocyst. 2. Vogiia peniacattiha, one of the 

 CalycophoritUe. 11 Nectocalyces : p Polypites : i Tentacles. 3. Diagram of a 

 Calycophorid. a a' Proximal and distal nectocalyces ; h Somatocyst : c Cajnosarc ; 

 d HydrophylHum or bract ; e Medusiform gonophore :y"Polypite. The dark lines 

 in figs. I and 3 indicate the endoderm, the light line with the clear space indicates 

 the ectoderm. (After Huxley.) 



obliterate the internal cavity, and give the organ the appearance 

 of a cellular mass." — (Huxley.) The polypites in the Calyco- 

 pkoridce often show a well-marked division into three portions, 

 termed respectively the proximal, median, and distal divisions. 

 Of these, the " proximal" division is somewhat contracted, and 

 forms a species of peduncle, which often carries appendages. 

 The " median " portion is the widest, and may be termed the 

 " gastric division," as in it the process of digestion is carried 

 on. It is usually separated from the proximal division by a 

 valvular inflection of the endoderm, which is known as the 

 " pyloric valve." The polypites have only one tentacle " de- 

 veloped near their basal or proximal ends, and provided with 

 lateral branches ending in saccular cavities," and furnished 

 with numerous thread-cells. The proximal ends of the poly- 



