MECZNIKOW, ON ICHTHYDIUM, ETC. 247 
Ichthydina, whilst the peculiar bottle- or retort-like shape 
of the latter is entirely strange to the Turbellaria. The 
furcal appendages on the tail of Ichthydina present also a 
striking difference between them and the Turbellaria. In 
the same way the characteristic integuments show very con- 
stant and important differences. The outside covering of 
the Turbellaria consists of a soft epithelial tunic, whose cells 
are all or nearly all provided with vibrating hairs, amongst 
which there are comparatively seldom stiff feeling-hairs. A 
cuticula is wanting in all Turbellaria in Arhynchia, as well 
as-in Rhynchocela. I may state this the more safely in 
contradiction to Keferstein, who describes the Nemertina as 
having a cuticula, because I have searched in vain for it in 
all the Nemertina which I found in Heligoland. 
But the outside covering of the Ichthydina is quite different; 
these possess, as I have before stated, a firm cuticula, which 
consists of chitin, and which bears a number of different firm 
excrescences. The vibrating hairs of our animal are, in com- 
parison with those of Turbellaria, very closely distributed, 
and are also peculiar on account of their conjunction with 
the cuticula. These differences in the integument, which 
also give rise to the differences of form in the two groups, 
seem to be so striking that we may readily use them as proofs 
against the opinion of Schultze, whilst the anatomical 
properties also of these animals do not present any striking 
agreement. Besides this, I must remark that, as we have seen 
above, the peculiarly simple organisation of the Ichthydina 
cannot have so great a systematical worth as other naturalists 
think. If one were to consider the negative character, the 
want of muscles, nerves, and water vessels, of our animals as 
important in regard to their systematic position, we could 
use the same character in regard to Infusors, and, in fact, to 
all animals which show a like want. 
Neither can I agree with Ehlers’ idea above mentioned, 
since I can see no important reasons for the relationship of 
Ichthydina with Nematodes in the alimentary apparatus of the 
former. The winding of muscular tissue in the cesophagus 
is present in Rotatoria and Tardigrada, and the straight 
intestine in a number of lower animals. The secondary like- 
ness in the formation of the digestive organs loses all import- 
ance when we compare the other organs of the Ichthydina 
and Nematodes, which have nothing in common. 
From the foregoing remarks it is easy to see that I believe 
the nearest allies of our animals to be the Rotatoria. This is 
shown, not only by the above attempts at combating the 
ideas of Schultze and Dujardin, but also by a nearer com- 
