Trochosphsera wquatorialis. By Herr Semper. 239 
organ (1 T) taking its rise, with a broad edge, from a flat hollow on 
the oral hemisphere close under the skin, but free in the cavity 
of the body ; it lies obliquely under the equator, then crosses into 
the aboral hemisphere, and here fastens itself to the skin by means 
of a number of thin filaments. Besides the nerve already men- 
tioned, this is the only organ which in part lies in the aboral 
hemisphere. I now pass on to a particular description of the 
several organs. 
As regards the histologic composition of the skin, I can give 
but little informatior^, I am sorry to say. On the whole it is very 
thin, yet the cuticle is tolerably resistent, and can still be observed 
in animals preserved since 1859 in glycerine. It is only at the 
equatorial fringe that any noteworthy thickening appears (Fig. 6). 
Here I could easily detect two layers, which will no doubt allow of 
being taken for cutis and epidermis, although I have taken down 
no written notes on their connective or cellular nature. With the 
exception of the circular fringe and a second small fringe leading 
to the mouth, the skin is perfectly free from hair. A real layer of 
skin muscles is entirely wanting. The circular fringe itself is, as 
already said, interrupted at one place (6?>) diametrically opposite 
the mouth, yet only partially interrupted. Whilst the fringed arc 
on each side ends in a blunted point (6 a, a'), both these are joined 
by a narrow bridge (6 h), which shows the same two layers as the 
circular fringe itself, but is thinner and has no cilia. The cilia of 
the equator are tolerably long, and under the microscope exhibit 
the motion belonging to all snail larvae, but no rotatory phenomenon. 
Still, through its relation to the second small fringe leading to the 
mouth (3 o), it is proved that this equatorial fringe really is the 
homologue of the rotatory organ of the Eotatoria. It further 
follows that the aboral hemisphere corresponds to the flat part 
situated between the creeks made by the fringe in Floscularia, i. e. 
to the forehead, whilst the oral corresponds to the real body of all 
other footed and footless Eotatoria. It thus becomes impossible to" 
denote the parts of the body in a way that would apply to all the 
different forms of Eotatoria. 
The muscular system is very meagrely developed. Besides those 
which, situated at the pharynx and at the head of the pharynx, 
belong to the tractus, undoubtedly developed muscles are only 
found at the mouth and anus. Two broad muscle-bands at the 
head of the pharynx, which have places of junction with skin in 
the oral hemisphere, have a forward pull (3 m, m'). A single 
(unmatched) muscle in the oral hemisphere acts as suspensory 
ligament to the oviduct and anus, both of which it joins simul- 
taneously (9m). The muscles are smooth, and of a yellow trans- 
parency. Probably the two broad ribbons mentioned above, which 
lie in the two quadrants nearest to the mouth yet connect the 
VOL, XIV. s 
