MECZNIKOW, ON ICHTHYDIUM, ETC. 243 
In the summer of 1863, during my stay in my fatherland 
(Charkow), I noticed a single example of this, which was 
equal in size to Chetonotus larus, and which I name Chetura 
(nov. gen.), capricornia (nov. spec.). It was found in a 
marsh. (Pl. V, figs. 2 and 3.) 
Another form of the family Ichthydina is also known to 
me from a single example which I noticed in Giessen in the 
autumn of the following year. This is a small species, 0°08 
mm. long, which I name Cephalidium (nov. gen.) longisetosum 
(noy. spec.). It is also bottle-formed, and has a blunted 
broad head, whose foremost end has a distinct mouth-appa- 
ratus, and is provided all over its surface with long vibratile 
hairs. To the head follows a thin neck, which joins itself to 
the body; this is provided on the dorsal surface with very 
long and strong bristles, and on the ventral surface with 
small vibrating hairs; at the posterior end there are no furcal 
appendages, but on the side of it right and left there is a 
bristle placed on a little knob, which represents without doubt 
a sensory organ (fig. 4). 
As regards the anatomical properties of the forms described, 
I must remark that there is generally no complexity or in- 
tricacy. The cuticula of the Ichthydina protects them from 
reagents, as in Rotatoria and many Infusors. It is easily 
dissolved in sulphuric acid, whilst in other acids, and even in 
alcohol, this is not the case. At least, I may so say from 
experiments which I have performed in a different way to 
other naturalists. I have placed animals which were being 
treated with a solution of ammonia into this fluid, together 
with sand granules, and was still able to distinguish the very 
fine and comparatively generally opaque cuticula, because 
through the contact with the sand granules the outline of the 
cuticula became plain. 
The cuticula in most of the bristleless kinds is provided 
with fine diagonal stripes. Under the cuticula lies a granular 
layer which passes directly into the parenchyma, formed of 
simple grains. In this I could find as little trace of muscles 
and nerves as my predecessors ; although these observations 
do not in any way shut out the possibility of there being 
such formations, yet their non-presence seems to be nothing 
unnatural ; it is satisfactorily known that very young embryos 
perform the same motions by means of different tissues 
which are performed by the muscles in the adults. I need 
only call to mind the Nematodes, among which there are 
forms which even when in an adult state permit no signs of 
muscles to be seen. 
One could say the same in regard to the nervous system ; 
