Trochosph^ra mquatorialis. By Herr Semper. 241 
tlie break in the fringe, divides it into four quadrants exactly. The 
optic nerve is the one branch of nerve No. 4 (5, 4 a) ; this swells 
into a very lengthened club-shaped ganglion (5 g) ; close upon it 
stands the eye furnished with a round lens (5 h) and with a semi- 
spherical covering of pigment closely enveloping it (5 b). The 
second branch of the same nerve also swells into a ganglion (5 d) 
situated near the eye-ganglion ; in this, however, in spite of all my 
pains, T could find no particular final organs or elements, which 
might have explained the meaning of this organ. 
Just as little do the other already mentioned final organs of 
nerves 3 and 6 allow of a certain explanation. The two nerves 3 
bend round, as I have already said, behind the muscle-layer to the 
anal pole and end here (1, 4 3 6), crossing the canals of the organ 
of excretion (7), in an oval sweUing (7 e) with a number of large 
ganglion-cells and a very small bright body of dark contour (7/), 
which is situated on the rather pointed end of the ganglion, and rises 
close upon the skin. Whether a fine hair (for feeling or hearing 
perhaps ?) is upon it, I could not distinguish, having no immersion 
lens. Quite similar too is the structure of the final organ of the single 
nerve No. 6 (Qh). The ganglion is here less large, deeply indented, 
and contains ganglion-cells both fewer and smaller ; on the blunt 
end, rising close upon the skin, the bright extreme body is here too 
found, as in the two other organs. Even though a more minute 
specification of the nature of these bodies is impossible, yet there 
can be no doubt, after the description just given, that they belong 
to that series of sense-organs, still somewhat problematical, which 
have lately engaged such especial attention. One may well think of 
the pedunculated sense-organ situated behind the forehead in many 
Eotatoria, and, as is well known, more minutely described by Leydig ; 
its position too allows it to be treated as homologous with these, for 
the three organs of the Trochosphsera all belong to the oral surface, 
and do not therefore lie on the forehead, but outside the circle of 
fringe : just as in the case of Rotifer {vulgaris), (fee, the organ adduced 
does not lie on the surface of the rotatory organ — the forehead — 
but behind it. For the rest, the morphological comparison of sense- 
organs, at least in the case of animals without a vertebra, is always 
unsatisfactory, since it is well known that among them organs 
physiologically equivalent — eyes, ears, &c. — may often occur in 
the most various parts of the body, that can be by no means mor- 
phologically compared together. I will only instance here the 
most striking example, the occurrence of eyes on the belly of 
Euphausia ; a discovery, however, which was not, as Gegenbaur 
in the second edition of his Comparative Anatomy wrongly states, 
first made by Claus, but by me. 
Close under the equatorial fringe lies a small indented fringe of 
hair (3 o) which leads into the hollow of the mouth and serves only 
s 2 
