ANNULATA. 223 
b) Body smooth. 
Stylochus EHRENB. Eyes numerous, all or most of them sup- 
ported by dorsal tentacles. 
Leptoplana KuRENB. 
Planaria Exrens. (Species of genus Planaria Muni.) Pla- 
narta and Dendrocelum Orrst. Hyes two or a row of many eyes 
in the anterior margin of the body. Oral aperture in the middle of 
the body. 
Sp. Planaria lactea MUELL., Zool. dan. Tab. tog, figs. 1, 2, Planaria torva 
MUELL., ibid. figs. 5,6; Planaria nigra MUELL., figs. 3, 4, all in fresh- 
water. 
Polycelis HHRENB. (and Prosthiostomum QUATREF.) 
Tetracelis EHRENB. 
Tricelis KHRENB. 
Monocelis KHRENB. 
Note.—On these, and some other genera all of which are not yet 
sufficiently limited, consult Enrenpera Symb. phys. Anim. evertebr. 
exclusis insectis, 1., and OERSTED 1. 1. 
Family LU. Nemertini. Nutrient tube simple, with double 
aperture, anus terminal. Body elongate, extremely contractile, 
roundish, or depressed, indistinctly annulate. 
It is not without hesitation that, after OrRsTEp, we have given 
these characters of the family of the Vemertini, whilst amongst the 
different writers, with respect to the true nature of the distinct 
parts, a remarkable variety of opinion prevails, so that it is un- 
certain whether the aperture, considered as anus, really belongs to 
the intestinal canal. Beneath the skin in these worms muscular 
fibres are seen, of which the external layer runs longitudinally, the 
innermost annularly or transversely. A canal of uniform width, by 
many supposed to be the intestine, runs straight through the body 
(DELLE CutAsE, Huscuxe, RaruKe). On its dorsal surface lies a 
canal, which is closed at its termination backwards, becomes narrower 
forwards and ends in a long proboscis. This part is, according to 
QUATREFAGES, the proper intestinal canal, which consequently has 
no anus. HUSCHKE supposed it to be an organ of propagation 
(testis ?) and the proboscis an external copulative organ ; hence the 
