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MANUAL OF ZOOLOGY. 



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

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

 termed respectively the proximal, median, and distal divisions. 



Fig. 54. Morphology of the Oceanic Hydrozoa. i. Diagram of the proximal extremity 

 of a Physophorid; a Pneumatocyst. 2. Vogtia pentacantka, one of the Calyco- 

 phoridce: n Nectocalyces; / Polypites; t Tentacles. 3. Diagram of a Calyco- 

 phorid: a a! Proximal and distal nectocalyces; b Somatocyst; c Coenosarc ; d 

 Hydrophyllium or bract; e Medusiform gonophore ; f Polypite. The dark lines in 

 figs, i and 3 indicate the endoderm, the light line with the clear space indicates the 

 ectoderm. (After Huxley.) 



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- 

 pites usually bear certain overlapping plates of a protective 

 nature, which are termed " hydrophyllia " or " bracts." They 

 are composed of processes of both ectoderm and endoderm 

 (fig. 54, 3 d), and they always contain a diverticulum from the 

 somatic cavity, which is called a " phyllocyst." The Calyco- 

 phoridce always possess swimming-bells, or " nectocalyces," by 

 the contractions of which the hydrosoma is propelled through 

 the water (fig. 54, 2). The nectocalyx in structure is very 

 similar to the "gonocalyx" of a medusiform gonophore, as 



