456 DR. MOXON ON THE ANATOMY OF ROTATORIA. 
These characters, but especially the second and fifth, serve to show that the rounded or 
arched side of the creature’s body is dorsal, the flattened side accordingly being ventral; 
for in no creature are the eyes on the ventral side of the alimentary tube, nor is the 
mouth in any turned to the dorsal side of the body. | 
In those Rotifers whose dorsal side does not differ in contour from the ventral, the 
corresponding side is nevertheless shown by the above-enumerated characters, which will 
always serve to determine the dorsal side of a Rotifer. 
Some Rotatoria lose part of these characters in adult life; for the eyes disappear in 
the stationary genera, and the mouth, in Floscularia and Stephanoceros, opens out as a 
great bell-shaped cavity, whose wide orifice is but slightly if at all turned to the ventral 
side; yet these Rotifers whilst young and in the freely moving state have the eyes, 
mouth, and dorsal feeler in their normal relation to each other. Under any circum- 
stances the dorsal side may be determined by the opening of the cloaca there, or by the 
position of the median feeler always on the dorsal middle line. : 
This median feeler has up to the present time been overlooked in many genera ; it has 
never yet been described in Melicerta, Floscularia, Metopidia, Limnias, or Pterodina. 
In these I am able to affirm its presence. Its existence has been already pointed out by 
others in Rotifer, Salpina, Euchlanis, Hydatina, and Philodina; but its constant position 
on the dorsal median line has, I believe, never been remarked. 
But this dorsal feeler must be carefully distinguished from the lateral feelers of 
stationary Rotatoria, which are conspicuous in Melicerta, and have been known as long 
as that Rotifer itself. Lateral feelers are present also both in Limnias and Floscularia ; 
and it is highly probable that they exist in all the stationary genera, though I have not 
as yet had an opportunity of observing other kinds than those named. 
These lateral feelers are symmetrically placed on the sides of the creature's body, 
towards the ventral aspect, and close to the part which forms the upper end when the 
lobes are retracted. In Melicerta (Pl. XLVII. fig. 2) they are raised on stalks, and their 
anatomy has been well described by Professor Williamson and other observers. In 
Limnias (fig. 3) they have the same structure, but are placed on slight conical elevations, 
and so likewise in Floscularia (fig. 1); but in the last-named genus the organ is smaller 
in proportion to the bulk of the animal than in either of the other instances, and offers 
the additional peeuliarity of having its setze curved in the direction of the tail. 
The setze of the dorsal feeler are shorter and less conspicuous than those of the lateral, 
whilst the circular space on which they are set is larger in the dorsal, The three feelers 
of Floscularia have hitherto been entirely overlooked, as have those of Limnias. 
In Philodina (fig. 4) and Rotifer the dorsal feeler is raised on a stalk, and much 
resembles a lateral feeler of Melicerta; but the true dorsal feeler of Melicerta (fig. 2), 
which has hitherto wholly escaped observation, is sessile on the back of the head, behind 
and between the eyes in the young, and on the same side of the body as the cloacal 
opening. It corresponds to the pedunculated dorsal feeler of Philodina in every par- 
ticular of these relations, which fully suffice to establish a true homology between the 
two organs, 
Hence, to properly compare these Rotifers, as done in a recent monograph, it will be 
