476 



POLYZOA. 



another, they are only aggregated, being lodged in distinct tubular 

 cells. The body of each animal appears to consist of a digestive canal 

 constricted once or twice in its course, and terminated by an anal orifice. 

 When these creatures 

 are extended, the upper 

 part of the body pro- 

 trudes from the cell, 

 the tentacular appara- 

 tus being supported on 

 a kind of neck, whereon 

 the mouth (a) is easily 

 and near it the 



Cristatella mucedo. 1. Egg, natural size. 2. Egg, magnified. 

 3. Animal after its escape from the egg : a, the mouth ; b, open- 

 ings of cell; c, the stomach; d, shell; e,f, ciliated tentactda. 



anus. 



(1246.) On each side 

 of the mouth the body 

 divides into two arms, 

 which, when spread 

 out, resemble a horse- 

 shoe, being flattened 

 and blunt ; and upon the arms are arranged about a hundred slender, 

 transparent, retractile tentacles, disposed on each side and upon the 

 summit like the barbs of a feather, and all covered with an infinite 

 number of cilia, whose action produces currents directed towards the 

 mouth, hurrying in that direction organized particles contained in the 

 water. 



(1247.) The three individuals that thus inhabit the same general 

 covering are produced at two distinct generations the two lateral being 

 the offspring of the central one, derived from it by a process of gemma- 

 tion ; but, when complete, they are evidently quite separate from and 

 independent of their parent. 



(1248.) The number of the tentacular appendages varies very con- 

 siderably in different genera : in Paludicella and Fredericella, which 

 have the fewest, there are about twenty, while in Alcyonella, Plumatella, 

 and Cristatella (fig. 241) there are as many as sixty, or even more. 

 In Paludicella the arrangement of the tentacula is infundibular ; but in 

 Lophopus, Alcyonella, Plumatella, and Cristatella (fig. 241) they assume 

 the shape of a horse-shoe. In Fredericella (fig. 242) they are united 

 together for one-half of their length by means of a delicate membrane. 



(1249.) The digestive apparatus in all these different genera consists 

 of an oesophagus, of a stomach, which forms a cul de sac, and intestinal 

 tube. The intestine is always straight, and without convolutions. Its 

 cavity is separated from that of the stomach by a pyloric valve that 

 completely closes the aperture ; whilst the oesophagus is in like manner 

 provided with a fold, situated sometimes near its middle, sometimes at 

 its lower part, that performs the office of a cardiac valve. 



