80 M. Hesse on a new Parasitic Crustacean. 
complete immobility, its useless locomotive appendages have 
become almost null or rudimentary; but, as it must provide 
itself with nourishment, it has, on the contrary, been completely 
furnished with everything that could be necessary to it for this 
purpose. We remark, in fact, that round the buccal orifice, 
which, from its proboscidiform structure, may furnish it with 
the means of absorbing liquids, there exists an auxiliary series 
of mandibles, arranged circularly and fitted, in case of necessity, 
to triturate solid objects, and that this organ is not only accom- 
panied by palpi, but also by prehensile feet destined to aid them. 
Thus, therefore, notwithstanding its apparent nakedness, it is 
not the less true that it has been very completely provided for 
its needs. 
And thus we have arrived at the most arduous portion of our 
work, which consists in finding the place in classification which 
must be assigned to our parasite. 
It may be seen, indeed, from the description that we have 
given of it, that the characters upon which we depend are not 
very strongly marked; we may add that they were still more 
difficult to ascertain, in consequence, as already stated, of the 
opacity of the body of this Crustacean, which is comparatively 
very thick, and of its cylindrical form, which renders it very 
unstable on the slide, where it does nothing but roll about ; 
hence, notwithstanding the long practice we have had with the 
microscope and the compressorium, we are not quite sure of 
having triumphed over these obstacles. Nevertheless, having 
operated upon a great number of individuals, and repeatedly 
verified our observations, we hope that in case we should have 
committed some errors, these will not be of much importance. 
At the first glance, seeing the simplicity of structure of the 
parasite, we asked ourselves whether we really had to do with a 
Crustacean. Subsequently, after having attentively examined 
it, we perceived that it could only belong to this category, and, 
this being the case, that, from the primitive state of its organs, 
it must be referred to the lowest rank in the classification of 
these Articulata, and placed among the Lerneocerea. This 
opinion once admitted, we had to seek for the characters which 
might justify this view; and the following are those which seem 
to us to do so. 
When we compared it, for example, with Lernea branchialis, 
we were struck at once by the resemblance which exists between 
their buccal systems: this part in each is proboscidiform, and 
composed of a retractile siphon forming a sucker, which shelters 
itself between the projecting rounded margins protecting the 
two sides of the aperture of the mouth. We find also that, as in 
Lernaa, this orifice is surrounded by auxiliary feet, and, lastly 
