134 
ZOOLOGY, 
Crass ITI.—Roratoria (Rottfers). 
General Characters of Rotifers.—The Rotifers, or wheel- 
animalcules, are abundant in standing water, in damp moss, 
etc., and in the ocean, and are so transparent that their in- 
ternal anatomy can be studied without dissection, while they 
are so minute, being from one fortieth to three hundredths 
of an inch in length (3 to $ mm.), that high powers of the 
eg! 
Fig. 91. —Squamella oblonga, magnified 200 
diameters. A view from below; shell or cara- 
pace (s, x1, s2); 8, the anterior transverse edge 
of the carapace; s', the anterior, and 52, the 
posterior corners of the carapace; s°, the border 
of the oval, flat area which occupies the lower 
face of the carapace: Jd, the cilia-bearing velam 
of the head; ¢, the fork of the tail (¢1) ; m, the 
mouth ; /, jaws ;j', muscles which move j; s¢, 
stomach ; ev, the contractile vesicle, or heart of 
the excretory system ; cv', cv?, the right, and 
cv3, cv’, the left excretory vessels ; eg, eg}, eg?, 
two largely developed young.—After Clark. 
the velum of the larval mollusk. 
microscope are needed in 
studying them. They are 
of special interest from 
the fact that after being 
dried for months to such 
a degree that little if any 
moisture is left in the 
body, they may be revived 
and become active. Pro- 
fessor Owen has observed 
the revivification of a 
Rotifer after having been 
kept for four years in dry 
sand. 
As an example of the 
ordinary type of Rotifer 
we may cite Sguamella 
oblonga (Fig. 91), which 
is allied to Brachionus. 
The characteristic organ 
of the wheel-animalcules 
is the velum (Jb) or pair 
of ciliated wheel-like flaps 
on each side of the head, 
which is comparable to 
By means of the rotatory 
movements of this velum the creature is whirled swiftly 
around. The body is broad and flattened, with the walls 
often dense, chitinous, sometimes shell-like, and variously 
sculptured, or the animal may be long and worm-like, as in 
Rotifer vulgaris (Fig. 92). 
The body is composed of several, 
