CHAPTER XII 



Moss ANIMALS AND LAMP SHELLS 

 Subkingdom MOLLUSKOIDEA 



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 Molluskoidea, is still far from settled. The Brachiopods were long placed 

 with the Mollusks, and the Bryozoa with the Corals and Sponges; but fuller knowl- 

 edge 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 are 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 resemblances 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 figure on p. 3391, which shows, greatly magnified, the ex- 

 ternal 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 de- 

 tached 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 of tentacles (a) to be protruded as in the figure, or to be withdrawn by means of mus- 

 cles^). 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 (#). The alimentary canal, which com- 

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

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

 again toward 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 attachment 

 (3390) 



