180 ZOO war. 



with tlie Polyzna, Bracldopods, and possibly the Mollusca, 

 the latter branch being probably a modified rermian type, 

 and with an ancestry not unlike that of the Eotifers and 

 aberrant, generalized Polyzoa and Brachioijoda. The classi- 

 fication of the Rotatoria is in an unsettled state, the gi'oup 

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

 the Echinoderidm, and Gastrotricha. 



Class III. —ROTATORIA. 



Worms with umiaUy mare or less solid segments, TeryuneguaMy dexdaped, 

 hearing a ciUaied velum. Vie mouth opening into a mctsta^ ; sexes separate, 

 the males much smaller, more rudiTnemtary than tItefemaZes. A small 

 nemous ganglion. No circulatory apparatus, hut with a voluminous excre- 

 tory {water-vasffular) organ. 



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

 highest form, Floscularia.) 



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

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



Class V7. — 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. 124, Membranipora 

 solida Pack.). Certain deep-water species 

 gi'ow in coral-like forms (Fig. 125. Myrio- 

 zouin subgracile D'Orbigny), while the 

 chitinous or homy Polyzoa (Fig. 126, 

 HalopMla iorealis Pack.), are often mis- 

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

 ma , en argt . Seitularian 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 tliat the latter name has priority. 



