180 ZOOLOGY. 



with the Folyzoa, Bracliiopods, and possibly the Mollusca, 

 the latter branch being probably a modified Termian type, 

 and with an ancestry not unlike that of the Kotifers and 

 aberrant, generalized Polyzoa and BracMoiMila. The classi- 

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

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

 the jEchinoderidce, and Gastrotricha. 



Class III. —ROTATORIA. 



Worms with usually more or less solid segments, very unequally developed, 

 hearing a ciliated velum, the mouth opening into a mastax ; sexes separate, 

 the males much smaller, more rudimentai-y than tite females. A smaM 

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

 tory (water-vascular) organ. 



(Albertia, Asplanchna, Hydatina, Bracliionus, Rotifer, aud the 

 highest form, Floscularia.) 



Laboratory Work. — The Rotifers can only be studied while alive and 

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



Class IV. — Polyzoa [Moss Ardmals). 



The Polyzoa, though not commonly met with in fresh 

 Avater, 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. 124, Membranipora 

 solida Pack.). Certain deep-water species 

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

 zoum suhgracile D'Orbigny), while the 

 chitiuous or horny Polyzoa (Fig. 126, 

 Halophila borealis Pack.), are often mis- 

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

 ma,, eB argt , Sertulariaii 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. 



