12G COMPARATIVE ANATOMY. 



Trematoda. 



Distoma, Monostomum, Tristoma, Polystomum, Aspidogastcr, Diplo- 

 zoon, Gyrodactylus. 



Cestoda.* 



Caryophyllajus, Ligula, Bothryoccphalus, Tamia, Tetrarhynchus. 



Neinertina (Rlrynclioccela). 



Pelagouemertcs, Ncmertes, Polia, Borlasia. 



II. Nematlielraiuthes. 

 Nematodes. 



Rkabditis, Dorylaiinus, SU'ongylus, Ascaris. 



Gordiacea. 



Gordius, Meroiis. 



III. Cheetognatlii.t 



Sagitta. 



IV. Acautliocephali. 



E chinorhynclius . 



V. Bryozoa.J 



Pliylactolasrna. 



Cristatella, Alcyonella, Lophopus, Pluinatella. 



Gyinnolosnia. 



Crisia, Homera, Alcyonidium, Flusfcra, Escliara. 



VI. Rotatoria. 



Hydatina, Notommata, Brachionus, Melicerta, Floscularia. 



VII. Enteropneusti. 



Balauoglossus. 



VIII. Gephyrea.§ 



Inermes. 



Sipunculus, Pliascalosoma, Priapulus. 



Cliastiferi. 



Ecliiurus, Bonellia. 



IX. Annulata. || 



* The Cestocla arc derived from a form common to them and to the Trematoda. 

 The difference in organisation is due to their different kind of parasitic habits. There 

 are several forms of which it is doubtful whether they belong to one or the other 

 division (Amphiptyehes). 



f The Cha?toguathi must not be regarded as allied to the Nemathelminthes because 

 they are put next to them ; the same remark holds gqod for the Acanthoccphali. 



% Pedicellina and Loxosoma are genera allied to the Bryozoa, and they might well 

 be united with them into one division, but they must not bo subordinated to them. 



§ In both divisions of the Gephyrea thore is a large number of very divergent 

 forms. 



|| Tomopteris, Myzostoma, and Polygordius are special forms, allied to, but very 

 divergent from, the Annulata. The last mentioned unites the characters of the 

 Nemertina and Nematodes with those of the Annelides. 



