3398 MOSS ANIMALS AND LAMP SHELLS 



though capable of slow locomotion, Loxosoma appears seldom to move from the 

 place once chosen. It feeds on microscopic particles, brought by the stream of 

 water kept up in the cavities of the sponge it inhabits. This food is conducted to 

 the mouth by the cilia of the tentacles and by a ciliated furrow round the tentacle 

 disc. The method of reproduction of this animal is remarkable. Two lateral buds 

 are seen on the mother in the illustration on p. 3397. The young animals quickly 

 and without any metamorphosis attain the form of the parent, and may, even while 

 attached to her, feed independently, only falling off when mature, and becoming 

 attached in her neighborhood. This is not, however, the only manner of reproduc- 

 tion. From time to time, without any interruption in the lateral budding, fertilized 

 eggs ascend from the ovary toward the tentacle disc, and develop into larvae which 

 in no way resemble Loxosoma. They have flat, almost shield-shaped bodies, sur- 

 rounded by a ciliated margin. After breaking out through the disc of the mother, 

 at the stage represented in the illustration, they pass through various changes be- 

 fore reaching the adult form. 



THE LAMP SHELLS Class Brachiopoda 



We must now leave the moss animals, about whose relationship to the rest of 

 the animal kingdom we know so little, and pass on to the equally enigmatical class 

 of the arm-footed animals, or Brachiopoda. The chief structural feature in the 

 Brachiopods which led to their being classed as mollusks, was their bivalve shell. 

 They were therefore regarded as a subdivision of the bivalves. How easily a 

 Brachiopod might be mistaken for a mussel will be understood by the reader who 

 glances at the following illustrations. But whereas the shells of the mussel 

 are at the animal's sides, and close in front, behind, and below, the hinge being on 

 the back, in the Brachiopods one shell is on the back and the other underneath. 

 There are, in addition, other profound differences in the anatomy of the soft parts. 

 A further argument against there being any relationship between the Brachiopods 

 and the mussels is found in the fact that no intermediate forms exist which could 

 facilitate the deduction of the one class from the other. On the other hand, many 

 zoologists are inclined to consider the Brachiopoda to be modified worms, a view 

 confirmed by their anatomy. Although there is little to record of the activities 

 of these creatures, they are worthy of attention, not only on account of their 

 structure, but also from their extraordinary stability. With regard to this latter 

 point they are almost unique in the animal kingdom (if we omit the lowest 

 unicellular organisms), in having remained essentially unaltered from the earliest 

 geological epochs. They have neither progressed or degenerated, but have lived 

 on practically at a standstill, so far as organization is concerned. The period in 

 which they flourished most is now long past. Not only in the number of species, 

 but also in the number of individuals were they once so rich that thick layers of 

 rock have been built up by their accumulated remains. Brachiopods are divided 

 into two orders; those having shells without hinges, and those with shells hinged 

 together. Taking the latter order (Testicardines) first, a few of its most important 

 families may be described. 



