180 zooLoar. 



with the Polyzoa, Brachiopods, and possibly the Mollusca, 

 the latter branch being probably a modified vermian type, 

 and with an ancestry not unlike that of the Kotifers and 

 aberrant, generalized Polyzoa and BrachiojJoda. The classi- 

 fication of the Rotatoria is in an unsettled state, the group 

 probably consisting of three orders, viz. : the true Rotatoria, 

 the BchinoderidcB, and Gastrotricha. 



Class III.— KOTATORIA. 



Worms with usually mc/re or less solid segments, very unequally developed, 

 bearing a ciliated velum, tJie mouth opening into amastax ; sexes sepa/rate, 

 the males much smaller, m/rre rudim^ntai-y than the females. A small 

 nenous ganglion. No circulatory apparatus, but with a voluminous excre- 

 tory (water-vascular) organ. 



(Albertia, Asplanchna, Hydatiua, Bracliionus, Rotifer, and the 

 highest form, Flosoulavia.) 



Lahoratm-y Work. — The Rotifers can only he studied whUe alive and 

 as transparent objects. Little is known about the American species. 



Class IV. — Poltzoa (Moss Animals). 



The Polyzoa, though not commonly met with in fresh 

 water, are among the commonest objects of the seashore. 

 They are minute, almost microscopic creatures, social, grow- 

 ing in communities of cells (called poly- 

 zoaria or corms), forming patches on sea- 

 weeds and stones (Fig. 134, Membraoiipora 

 solida Pack.). Certain deep-water species 

 grow in coral-like forms (Fig. 125, Myrio- 

 zoum subgracile D'Orbigny), while the 

 chitinous or horny Polyzoa (Fig. 126, 

 Halophila borealis Pack.), are often mis- 

 Pig. 124.— Cells of Sea- taken for sea-weeds on the one hand, and 

 ma , en arge . Sertulariau Hydroids on the other. From 

 their likeness to mosses the name Bryozoa was given to the 

 group by Ehrenberg, a year after Thompson (1830) had 

 called them Polyzoa, so that the latter name has priority. 



