76 INVERTEBRATE ANIMALS. 
outwards. In the substance of the disc run at least four canals, 
which communicate with the cavity of the coenosarc, and pro- 
ceed to the margin of the bell, where they all open into a cir- 
cular vessel. The mouth of the bell is also furnished with 
a delicate ledge, which runs round its circumference, and is 
known as the “veil.” The structure, therefore, of the necto- 
calyces, is very similar to that of an ordinary medusiform 
gonophore, the chief difference being the absence in the former 
of the central polypite or manubrium. The nectocalyces are 
highly muscular, and have the power of alternately contracting 
ry 
Fig. 23.—Morphology of Oceanic Hydrozoa. 1. Diagram of the proximal end of 
a Physophorid; a Float: 2. Vogtia pentacantha, one of the C alycophoride ; n 
Nectocalyces ; 4 Polypites; ¢ Tentacles: 3. Diagram of a Calycophorid; a a’ 
Nectocalyces ; 6 Proximal dilatation of the coenosarc; ¢ Coenosarc ; d Bract; e 
Medusiform gonophore; / Polypite (after Huxley). 
and dilating, thus driving the whole organism through the 
water. In Vogtza (fig. 23, 2), which may be taken as a good 
example of the group, the nectocalyces (7) are succeeded bya 
group of polypites (Z). Each polypite is furnished with a 
mouth opening into a digestive sac, which in turn communi- 
cates with the cavity of the coenosarc. In most instances, but 
not in Vogtia, each polypite is protected by a kind of over- 
arching plate, which is termed a “bract.’. The mouths of the 
polypites are not furnished with a circlet of tentacles, but each 
polypite has only a single tentacle developed from near its base. 
