138 ZOOLOGY. 
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 Rotifers and 
aberrant, generalized Polyzoa and Brachiopoda. The classi- 
fication of the Rotatoria is in an unsettled state, the group 
probably consisting of three orders, viz. : the true Rotatoria, 
the Lchinoderide, and Gastrotricha. 
Crass III.—ROTATORIA. 
Worms with usually more or less solid segments, very unequally developed, 
bearing a ciliated velum, the mouth opening into a mastaz ; sexes separate, 
the males much smaller, more rudimentary than the females. A small 
nervous ganglion. No circulatory apparatus, but with a voluminous excre- 
tory (water-vascular) organ. 
(Albertia, Asplanchna, Hydatina, Brachionus, 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. 
Crass IV.—Ponyzoa (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. 94, Membranipora 
solida Pack.). Certain deep-water species 
grow in coral-like forms (Fig. 95, Myrio- 
zoum subgracile D’Orbigny), while the 
chitinous or horny Polyzoa (Fig. 96, 
Halophila borealis Pack.), are often mis- 
Fig. 94 —Cells of Sea- taken for sea-weeds on the one hand, and 
mat, enlarged. Sertularian 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. 
