126 ' COMPARATIVE ANATOMY. 



Trematoda. 



Distoma, Monostomum, Tristoma, Polysfcomum, Aspidogaster, Diplo- 

 zoon, Gyrodactylus. 



Cestoda.* 



Caiyopliyllasus, Ligula, Bothryoceplialus, Ttenia, Tetrarhyachus. 



Nemertina (Rhyncliocoela). 



Pelagonemertes, Nemertes, Polia, Borlasia. 



II. Nematlielrainthes. 

 Nematodes. 



Rhabditis, Dorylaimus, Strongylus, Ascaris. 



Gordiacea. 



Gordius, Mermis, 



III. CliEetognatlii.t 



Sagitta. « 



rV. Acanthocephali. 



Echinorhynchus, 



V. Bryozoa.J 



PhylactolEema. 



Cristatella, Alcyonella, Lophopus, Plumatella. 



Gymnolasma. 



Crisia, Homera, AlcyouicUum, Flustra, Esoliara. 



VI. Eotatoria. 



Hydatina, Notommata, Brachiouus, Melioerta, Ploacularia. 



VII. Enteropneusti. 



BaJanoglossus. 



VIII. Gepliyi'ea.§ 



Inermes. 



Sipunculua, Phascalosoma, Priapulus. 



Chsetiferi. 



EcliiurnSj Bonellia, 



IX. Annulata.|| 



* The Cestoda are derived from a form common to them and to the Trematoda. 

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

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

 division (Amphiptyches). 



f The Chastognathi must not be regarded as allied to the Nemathekuiuthes because 

 they are put next to them ; the same remark holds good for the AcanthocephaU. 



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

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



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

 forms. 



II Tomopteris, Mysostoma, and Pohjgordius 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. 



