CHAPTEK XII. 

 MOSS-ANIMALS AND LAMP-SHELLS, Subkingdom MOLLUSCOIDEA. 



THE exact positions in the animal kingdom of the Bryozoa or moss-animals, and 

 the Brachiopoda or arm-footed animals, which are generally united under the name 

 of Molluscoidea, is still far from settled. The Brachiopocls were long placed with 

 the Molluscs, and the Bryozoa with the Corals and Sponges ; but fuller knowledge 

 made it evident that the Bryozoa did not in any way belong to the latter. Next, 

 they were classed with the Rotifers, or wheel animalcules, under the name of 

 Ciliata, as a kind of appendage to the worms, while by others they were grouped 

 with the Ascidians. They are here placed with the Brachiopoda, not because the 

 two groups are really related, but simply because they are alike in having no 

 established place in the classification of the animal kingdom. It is true that the 

 Bryozoans and the Brachiopods are sometimes classed together because of the 

 similarity of their development, and also for certain supposed anatomical resem- 

 blances between them ; but these latter are far from convincing, and the similarity 

 of their larval histories has been disputed. 



MOSS-ANIMALS, Class Bryozoa. 



The moss-animals almost always live in colonies, the individuals of which are 

 joined in a number of different ways to form stocks. The individual animals are small, 

 and the stocks generally also small, never forming anything approaching the masses 

 of substance yielded by those of the corals. The structure of the Bryozoan animal can 

 be studied in the accompanying figure, which shows, greatly magnified, the external 

 outline and the inner organs of a single individual belonging to the stock of a fresh- 

 water form (Paludicella) from Belgium. The individual figured has been detached 

 at its base from the one below it, and the one next above is broken off. The body is 

 represented by a chamber or cell, in this case somewhat elongated. Its walls are stiff, 

 except at the anterior end, where they are flexible enough to allow the crown of ten- 

 tacles (a) to be protruded as in the figure, or to be withdrawn by means of muscles 

 (m). One of these muscles is seen to be specially powerful, and runs through nearly the 

 whole length of the cell. The mouth is at the anterior end of the body, surrounded 

 by the circle of ciliated feelers or tentacles (a). The alimentary canal, which com- 

 mences with a muscular pharynx (6) hangs down in the form of a loop into the 

 body-cavity, the stomach (g) being its lowest portion. Its terminal portion runs 

 again towards the anterior end, so as to open not far from the mouth (at c). The 

 whole alimentary tube is but loosely fastened to the body- wall, its chief attach- 

 ment being by means of a single short strand at the end of the stomach called the 

 funiculus, and shown in the illustration. In all adults, two masses of cells are 



