BRYOZOA. 27 



Class III.— BRYOZOA. 



Char. — Tentacles of the polype hollow, with ciliated margins ; 

 alimentary canal with stomach, intestine, and anus ; 

 polypary, when present, external, horny, and calcareous. 



The metamorphoses which the Bryozoa undergo are like 

 those of the lower Polyiri ; the embryo developed from the 

 ovum is an oval, discoid, or subdepressed body, with a general 

 or partial ciliated surface, by which it enjoys a brief locomo- 

 tive life after its liberation from the parent. The Bryozoa are 

 allied to the compound Ascidia ; but not one of the ascidian 

 Molluscoids quits the ovum as a gemmule swimming by 

 means of cilia ; and no Bryozoon quits the ovum hi the guise 

 of a Cercarian or tadpole, to swim abroad by the alternate 

 inflexions of a caudal appendage. In a progressive and con- 

 tinuous series of teachings, by pen or word of mouth, the 

 place of an osculent or transitional group is governed by 

 convenience, by considerations of how best to teach by com- 

 parison and easy gradation. The real merits of the man who 

 would make scientific capital by changing the position of such 

 group, and by imputing error or ignorance to the author from 

 whom he may differ in this respect, are easily weighed and 

 soon understood. 



The Bryozoa, whether regarded as the highest organized 

 Polypes, or as the lowest organized Mollusca, or as an inter- 

 mediate type, are treated of in systematic palaeontology in the 

 position here assigned to them. The practical palaeontologist 

 finds himself compelled to arrange and study the fossil 

 Bryozoa along with the corals, if only on account of the diffi- 

 culty he, in many cases, experiences of determining to which 

 class of Polypi his specimens belong. M. d'Orbigny, who has 

 devoted much attention to this class, enumerates 544 fossil 

 species, distributed in 73 genera. Tin's number must be very 



