[ 455. ] 
XIX. Notes on some points in the Anatomy of Rotatoria. 
By Warrer Moxon, Esq., M.B., F.L.S. 
(Plate XLVII.) 
Read February 4th, 1864. 
THE object of this paper is to point out some important particulars in the structure of 
certain Rotatoria, which I hope will serve to supply certain deficiencies in the general 
and special anatomy of this interesting group of animals. 
In reading monographs on Rotifera, I have remarked an uncertainty in the determina- 
tion of the corresponding aspects of different forms: the terms dorsal and ventral are 
often used in describing their anatomy, but authors not uncommonly represent structures 
really dorsal as placed on the side, or even, in comparing genera, make the ventral side 
of one genus correspond to what is truly the dorsal side of another; yet the characters of 
the dorsal and ventral sides of Rotatoria are constant, and may be recognized without 
much difficulty. 
In every Rotifer there is a median plane, on either side of which the lever- and muscle- 
systems are symmetrically developed; the lines wherein this imaginary plane cuts the 
integuments above and below are respectively the dorsal and ventral median lines: we 
require to know which of these lines is dorsal and which ventral. 
Many actively moving genera have firm tunics, one side of which differs in an obvious 
way from the other; on the other hand, some roving, and all stationary genera are in 
transverse outline more or less rounded. In those roving genera which have one side 
arched and the other flat, it has long been well known that the intestine runs down on 
that side of the ovary which is towards the arched side of the body : the mouth in these 
Rotifers is always in that side of the cephalic disk which is towards the flat side of the 
body : the eye or eyes are always on that side of the alimentary tube which is towards the 
arched side: in the middle line of the same side is an organ which may be generally 
described as a small round space bearing motionless hairs or setæ; this organ may be 
sessile or it may be stalked, but it is constantly in one relative position ; and that is, on the 
same side of the cesophagus as the eye, and just on the anterior end of the body when the 
head is retracted : lastly, the cloaca—the common outlet of the intestine, ovary, and so- 
! pud water-vascular system—opens in the middle line on the arched side of the creature's 
ody. | 
Thus in these Rotatoria there are, as distinguishing characters of the arched side, 
Ast, the course of the intestine towards it; 2nd, the position of the eyes on that side of 
the csophagus; 3rd, the position of the median feeler (setze-bearing spot) on that side; 
4th, the opening of the cloaca upon that side; 5th, the mouth turned away from it; 
6th, further, it is to be noticed that the animal, in moving over surfaces, keeps the arched 
Side upwards, due | = 
pe 3N2 
