1876.] 19 [Minot. 



tlie wall of the digestive tube, he quietly assigns them to the paren- 

 chym! It is time that this hasty generalization, founded upon a 

 careless observation, be forgotten. 



The Platheltninths are all bilateral animals, and none of them 

 present any special points of resemblance to any of the Radiata; we 

 cannot therefore link the worms with any of the lower forms through 

 this class. Indeed the whole class presents a number of peculiari- 

 ties, sufficient to justify their temporary separation from all other 

 forms of animals, until their real affinities shall be discovered. 



The class was formerly divided as follows: — 



C Rhabdocoela, 5 



1. turbellarians 1 Dendroccela, 2. trematods. 3. cestods. 

 ( Nemertines. 



This division, however, cannot stand. The Nemertines are nowise 

 closely related to the Dendroccela and Rhabdoccela, but must be re- 

 moved entirely from the class and put by themselves, until their* 

 proper position shall be determined. Almost every organ of the 

 Nemertines is different from the corresponding organs in the true 

 Plathelminths. The epidermis is in both cases a ciliated cylindrical 

 epithelium with large unicellular glands, but this structure is char-, 

 acteristic of most aquatic invertebrates, that have no thick cuticula^ 

 but the singular Stabchetikorper that are so characteristic for the 

 Dendroccela and Rhabdoccela, are entirely unknown in Nemertines. 

 The muscular layers seem to be typically three in the former, four in 

 the latter; but on this point there is still much uncertainty, therefore 

 little weight can be laid upon it. The nervous system consists in 

 Nemertines of an anterior ring around the sheath of the proboscis.. 

 This ring gives off two large cords, each consisting of central fibres 

 and two strings of ganglionic cells. 1 There are no nervous ring nor 

 lateral cords known in Plathelminths, but only a single central gan- 

 glionic mass in the anterior part of the body, from which radiate 

 numerous small nerves. The two stout nerves, said by many authors 

 to run backwards from the ganglion, 1 have been unable to discover 

 in any of the twenty species I have examined, which agrees with 

 Moseley's 2 experience. 



By this observation the theory of the formation, phylogenetically, 



1 Hubrecht. Aanteekingen over de Anatomie, Histologic en Ontwikkelungsgesch- 

 iclite van eenige Neniertinen, Utrecht, 1874. 



2 Moseley. On the Anatomy and Histology of the Land Planarians of Ceylon. 

 Phil. Trans., 1874, p. 105. 



