244 MECZNIKOW, ON ICHTHYDIUM, ETC. 
if in our case its absence should seem to stand in contradic- 
tion to the important development of the sensory apparatus. 
Besides the presence already mentioned of complicated eyes 
and light-breaking bodies in Ichthydium ocellatum, the 
sense organs of these animals are represented by various 
sensitive hairs, such as the dorsal bristles of all kinds of 
Chetonotus (those bristle-formed elevations mentioned by 
Schultze in Turbanella, must also be reckoned among them), 
as well as the long bristles of Cephalidium, and those stiff 
erect hairs on the foremost part of the body (see in Ichthy- 
dium ocellatum, Plate V, fig. 1). To these belong also the 
above-mentioned fine bristles on the tail-end of Cepha- 
lidium. Besides this, the cuticula carries vibrating hairs, 
which in all sorts of Ichthydina are disposed on the ventral 
surface, and are present in Cephalidium, only on the head, in 
the form of long cilia. The vibrating hairs are either of that 
kind described by M. Schultze in his Chetonotus maximus 
(Schultzii), or are disposed as a simple covering of equal- 
sized hairs. Through the movement of these ventral cilia a 
current of the surrounding fluid is made, even when the 
animals themselves are at rest. 
The digestive apparatus is the same in all Ichthydina. The 
mouth opening at the fore end, on the ventral surface of the 
body, is surrounded with a chitinous ring which appears in 
some kinds of Chetonotus as a body provided with vertical 
thickenings. In Cephalidium the oral aperture is placed on 
an expanded plate, not being provided with a mouth-ring. 
The mouth leads into a narrow pharynx or cesophagus, which 
is provided with strong chitinous walls, and which is sur- 
rounded by a thick layer, in which in some species distinct 
square markings are seen, whilst in others it is perfectly 
homogenous. The true chylus intestine follows the esophagus. 
This runs straight to the anus placed on the back, and is 
provided with numerous oil-globules. 
With regard to their generative powers I must own that 
my knowledge is far from perfect. But this much is certain, 
that all those which I have examined are of different sexes, 
and not hermaphrodites, as those described by M. Schultze, 
which, perhaps, may be only impregnated females. The 
female generative organs of those individuals examined by 
me, which were old enough to enable me to distinguish the 
sex, have all the same simple structure which Schultze has 
described in his species. As I have discovered in Chetonotus 
larus, they produce two kinds of eggs, which are clearly the 
so-called winter and summer eggs, phenomena which have 
long been known in the Rotatoria. 
