ANNULATA. 223 



b) Body smooth. 



Styloclms EHRENB. Eyes numerous, all or most of them sup- 

 ported by dorsal tentacles. 



Leptoplana EHRENB. 



Planaria EHRENB. (Species of genus Planaria MUELL.) Pla- 

 naria and Dendroccelum OERST. Eyes 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. 109, figa. i, 2, Planaria torva 

 MUELL., ibid. figs. 5, 6 ; Planaria nigra MUELL., figs. 3, 4, all in fresh- 

 water. 



Polycelis EHRENB. (and Prosthwstomum QUATREF.) 

 Tetracelis EHRENB. 

 Tricelis EHRENB. 

 Monocelis EHRENB. 



Note. On these, and some other genera all of which are not yet 

 sufficiently limited, consult EHRENBERG Synib. phys. Anim. evertebr. 

 exclusis insectis, L, and OERSTED 1. 1. 



Family II. 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 OERSTED, we have given 

 these characters of the family of the Nemertini, 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 CHIAJE, HUSCHKE, RATHKE). 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 



