102 INVERTEBRATE ANIMALS. 
filled with a nutrient fluid. In the angle between the two 
canals which run from the base of the funnel to the surface is a 
little vesicle or sac, believed to be a rudimentary organ of hear- 
ing, and placed upon this is a little mass which is generally 
believed to be of a nervous nature. If this is correct, this is 
the first indication which we have hitherto encountered of a 
genuine nervous system. The reproductive organs are de- 
veloped in the walls of the canal-system. 
The only other form of the Ctexophora which deserves men- 
tion is the “Venus’s girdle” (Cestum Venerts), which agrees in 
essentials with Pleurobrachia, but is greatly elongated in a 
direction at right angles to the alimentary canal, till we have a 
ribbon-shaped body produced, four or five feet in length and 
two or three inches high. Cestwm is not uncommon in the 
Mediterranean, and has the power of phosphorescence, appear- 
ing at night as a moving and twisting band of flame. 
TABLE OF THE DIVISIONS OF THE CCRLENTERATA. 
Cuiass I. Hyprozoa.—The walls of the digestive sac not separated 
from those of the body-cavity. The reproductive organs external. 
Sub-class 1. Hydroida :— 
a. Hydrida.—Ex. Hydra. 
b. Corynida.—Lx. Tubularia. 
c. Sertularida.—Ex. Sertularia, Campanularia. 
Sub-class 2, Siphonophora :— 
a. Calycophoride.—Ex. Vogtia. 
¢.—Physophoride.—F:x. Portuguese man-of-war (Physalia). 
Sub-class 3. Discophora :— 
J. Meduside. 
Sub-class 4. Lucernarida :— 
g. Lucernariade.—Ex. Lucernaria. 
h. Pelagide.—x. Aurelia. 
t. Rhizostomide.—Ex. Rhizostoma. 
Sub-class 5. Graptolitidee. 
Crass II. Actrnozoa.—Digestive sac distinct from the general 
cavity of the body, but opening into it. Reproductive organs internal. 
Order 1. Zoantharia :— 
a. Z. malacodermata.—Ex. Sea-anemones (Actinidz). 
b. Z. sclerobasica—Ex. Antipathes. 
ce. Z. stlerodermata,—Ex. Brain-corals, Star-corals, and Madre- 
pores. 
Order 2. Alcyonaria.—Zx. Dead-men’s-toes (Alcyonium), Sea-rods, 
(Virgularia), Red Coral. 
Order 3. Rugosa.—(All extinct). 
Order 4. Ctenophora.—Zx. Pleurobrachia, Venus’s Girdle (Cestum). 
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