436 CHARACTERS OF INVERTEBRATE ANIMALS 



dated with the Vertebrata (pp. 297-300), the term Molluscoida 

 gradually fell into disuse, and the Moss- Polypes and Lamp- 

 Shells were cut adrift. There is good reason for thinking that 

 they are distantly related to the segmented worms, but their 

 relationships to that group and to one another are very obscure. 

 Perhaps the simplest plan will be to retain the old division 

 Molluscoida for their reception, provided the derivation of the 

 word ( = mollusc-like) be ignored. As Huxley himself has re- 

 marked, it is often necessary to retain terms, the derivations of 

 which have reference to obsolete views. The two included classes 

 — I. Moss-Polypes (Polyzoa) and 2. Lamp-Shells (Brachiopoda) — 

 are best considered separately. 



Class L— MOSS-POLYPES (Polyzoa) 



These are small aquatic animals which are for the most part 

 inhabitants of the sea, though some of them are found in fresh 

 water. They present a peculiarity which so far we have only 

 met with in some Tunicates (p. 300), i.e. they are colonial. From 

 the &g^ a free-swimming embryo is hatched, which after a time 

 becomes fixed and founds a colony by means of budding, in a 

 way suggestive of what takes place in plants. The shape of 

 the colony naturally depends upon the manner in which the buds 

 arise, and it may be compact, flattened, or branched in a more 

 or less elaborate way. There is a firm external skeleton for the 

 support of the colony, sometimes of gelatinous nature, but more 

 frequently of horny or calcareous consistency. Each member 

 of the community (zooid) is lodged in a special depression or cup, 

 and within the protective investment the bodies of the different 

 zooids are connected together. The Polyzoa are among those 

 animals included in the old group of " zoophytes " (Gk. zoon, an 

 animal; phyto, a plant), so named from the exploded idea that 

 they partook of the nature both of plants and animals, a notion 

 largely due to the fixed nature and plant-like appearance of many 

 kinds. Even yet some of them are popularly confounded with 

 sea- weeds, and of such one of the most abundant is the Sea- Mat 

 [Flustra) (fig. 269), the flattened branching skeletons of which 

 are among the common objects thrown up on the shore by the 

 action of the waves. Examination of one of these with a lens 

 reveals the presence of innumerable closely-packed little cups. 



