TURBELLARIA. 7 



both by Aristotle and Hippocrates — for they employed it, 

 technically, as equivalent to the intestinal worms — we come to a 

 fairer interpretation of the original Greek root (etXeoj) from which 

 the noun itself (eX/iw/s) is derived. At the same time, we legiti- 

 mately permit greater scope to the class-title, at once simplifying 

 the scheme of classification without disturbing the recognized 

 affinities of its subdivisions. 



In regard to the proposal of a new sub-class, this I conceive 

 to be a still more important desideratum ; for, not a few zoologists 

 still cling to the very erroneous notion that the Oestoda and 

 Acanthocephala are furnished with a digestive apparatus, whereas, 

 both these orders together constitute a group of entozoa quite 

 distinct from the Sterelmintha and Ooelelmintha. Neither the thorn- 

 headed worms nor the tape-worms are supplied with any mouth 

 or intestine, but their nourishment is obtained by a vicarious 

 process of imbibition through the general surface of the body. 



Having thus offered a simple and, I trust, a useful scheme 

 of classification, and having briefly explained my reasons for 

 its adoption, I proceed, without farther prelude, to take up the 

 various groups as they occur in the scheme, commencing with the 

 first order, namely, the Turbellaria, which may be arranged as 

 follows : — 



( PlanaridcB (Family I.) 

 TuKBBiLAKiA | ^g,„g^^j-^^ (Family H.) 



The Turbellarians were first collected into a single group by 

 the distinguished naturalist Bhrenberg, who recognized the pre- 

 sence of vibratile cilia over the entire surface of their bodies. This 

 important character was found to be common to all the members 

 of the group, and in consequence of the peculiar rotatory motion 

 communicated to the water whilst the animals were in the act of 

 swimming, the ordinal title in question was imparted to them. 

 Different writers have since employed the term Turbellaria in a 

 more or less restricted sense, as compared with the original value 

 imparted to it by Ehrenberg; but, on the whole, the modifica- 



