148 THE ROTATORIA. § 189. 
are two or three on each side, and sometimes there sre from five to eight 
airs,® but rarely more.® 
The lateral bands approach each other at the posterior extremity, and 
their canals join in a common, highly-contractile vesicle with thin walls, 
which empties externally its aqueous contents through the cloacal open- 
ing. 
kn orifice, situated usually upon the neck, and sometimes pedunculated, 
serves probably to introduce the water into the cavity of the body. This 
water enters the aquiferous system through the lateral vessels which float 
free in this cavity, and at last is expelled through the contractile vesicle. 
In this way, a constant renewal of water can occur, and the opening upon 
the neck may therefore be properly termed ‘a respiratory orifice or tube. 
There can be but little doubt that the rotatory organs also, have a respir- 
atory function, for their surface is covered with thin epithelium, and their 
cilia produce a constant change of the water. 
CHAPTER VIII. 
ORGANS OF SECRETION. 
§ 139. 
Some of the Rotatoria secrete a gelatinous substance, which, hardening, 
forms the cells and tubes into which they can partly or wholly withdraw 
themselves. The organ of this secretion is yet-unknown; but the secretion 
appears to be derived from the posterior extremity, and especially from the 
cloacal opening.© 
2 Notommata copeus, and syring. 
8 With Notommata clavulata, and myrmeleo, 
the number of these organs is remarkable ; each 
lateral band has thirty-six to forty-eight; see 
Ehrenberg, Die Infusionsthierchen, Taf. XLIX. L. 
4 Ehrenberg was the first to direct the atten- 
tion of naturalists to these two lateral bands and 
their contractile vesicles ; but he regarded them 
as two testicles with their vesiculae seminales 
(Abhandl. d. Berl. Akad. 1830, p. 51). The incor- 
rectness of this opinion, and which he has main- 
tained in his grand work, cannot be doubted, if it 
is considered that these two bands with their 
appendages are already developed and in activity 
with the young animals, and this even before they 
have escaped the cavity of the parental body. 
In all Ehrenberg’s published figures, one no- 
tices nothing of the flexuous canals of these or- 
gans, and which, therefore, he does not appear to 
have observed. 
5 The respiratory orifice is cervical with Entero- 
plea, Hydatina, Diglena, and many species 
of Notommata; but, with Rotifer, Philodina, 
Brachionus, and some species of Salpina, Euch- 
lanis, and Notommata, it is replaced by a tube. 
With Actinurus, exceptionably, a simple res- 
piratory tube is placed under the throat ; and with 
Tubicolaria, and Melicerta, there are two in the 
same region. 
1 With Conochilus, and Lacinularia, where 
several individuals are attached by their tails 
around a common centre, the nucleus of one of 
these colonies is formed by a loose, gelatinous sub- 
stance, in the cells of which these animals can par- 
tially withdraw themselves. With Oecistes, Tu 
bicolaria, Stephanoceros, Floscularia, and Lim 
nias, each individual occupies an isolated anc 
more or less hard gelatinous tube (Ehrenberg, Die 
Infusionsthierchen). The tubes of Melicerta, of 
which Schaffer has given an excellent figure (Die 
Blumen-polypen der siissen Wasser 1755, Taf. I. 
II.), are very remarkable, and according to Ehren ~ 
berg, are composed of brown polygonal cells which 
are excreted through the cloacal opening and 
glued together (Die Infusionsthierchen, p. 406). 
