THE HIGHER GROUPS. 575 



another very natural assemblage. But it must be admitted 

 that the highest forms of this division are separated by no 

 very sharp line of demarcation from the Armelida ; while 

 the simplest Turhellaria are ahiiost on a level with tiie Fhy- 

 semaria and the lower Ilydrozoa. Even a Flanarla is com- 

 parable to a free zoophyte ; its proboscis may be likened to 

 the hydranth of a 3Iedusa, the prolongation of the alimen- 

 tary sac to the gastro-vascular canals, the central nervous sys- 

 tem, with its lateral prolongations, to the marginal gangHa 

 and nerves. The water-vascular system and the com.plication 

 of the reproductive organs, indeed, afford clear marks of dis- 

 tinction ; but both of these systems vary indefinitely in the 

 degree of their development within the limits of the Turhel- 

 laria. 



On the other hand, the connection of the Ilirudlnea by 

 such forms a^ Malacohdella with the Turhellaria and Trenia- 

 toda is very close ; Polygordlus appears to be a transitional 

 form between the Turhellaria and the Folycha^ta ; while the 

 Motifera^ in many respects, represent larval forms of the 

 Polycha^ta and of the Gephyrea. 



The Cestoidea are usually regarded as anenterous Trema- 

 toda, in which case, of course, they must be associated with 

 the latter. 



I propose to establish a division of Tkiciioscolices for 

 the natural orders now enumerated, in order to discriminate 

 the morphological type which they exemplify frcm that of 

 the Nematoscolices, containing the Nematoldea^ which are 

 as remarkable for the universal absence of cilia as the former 

 are for their presence ; and which are further so clearly dis- 

 tinguished by the arrangement of their nervous and muscu- 

 lar systems and of their water-vessels ; and by their ecdysis. 



The connection between the two divisions by way of the 

 Nematorhyncha and the Fotifera is undoubtedly very inti- 

 mate, and there is almost as much reason to arrange the N^e- 

 matorliyncha with the Trichoscolices, as with the Nematosco- 

 lices. On the whole, however, I think that, notwithstanding 

 the cilia of the Gastrotricha^ the closest aifinities of the 

 Jsfematorhynclia are with the Neniatoidea, and I therefore 

 place them among the JSTematoscolices. 



But I. may remark, once for all, that the attempt to estab- 

 lish sharply-defined, large divisions of the animal kingdom is 

 futile. The progress of knowledge every day renders it 

 more and more clear that morphological groups are compara- 

 ble to distributional provinces ; each, however well marked 

 25 



