MANUAL OF ZOOLOGY. 



" 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. 

 1 8, 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. 18, 2). The nectocalyx in structure is very 



Fig. 18. Morphology of the Oceanic Hydrozoa. i. Diagram of the proximal ex- 

 tremity of a Physophorid. a Pneumatocyst. 2. Vogtia pentacantha, one of the 

 Calycophorida. n Nectocalyces ; / Folypites ; t Tentacles. 3. Diagram of a 



' Calycophorid. a a' Proximal and distal nectocalyces ; b Somatocyst ; c Ccenosarc ; 

 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.) 



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

 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 



