472 



GENERAL HISTORY OP THE INFUSORIA. 



all these particulars it, on the contrary, assimilates to the larvae of Vermes, 

 between which and the adult state the diversity is equally great. 



The accompanying tabular statement given by Yogt briefly presents the 

 chief points of the discussion. 



SYSTEMATIC POSITION OF THE EOTATORIA. 



Cohn's name may now be added to the list of opponents to the Crustacean 

 alliance. We have already seen (p. 447) that he denies the occurrence of any 

 metamorphosis in the course of development of the Eotatoria, and by so 

 doing sets aside one indication Leydig brought forward in favour of their 

 alliance with Crustacea. The following is a summaiy of his arguments against 

 that relationship : — " The ciliated condition of the E-otifera, their respiratory 

 apparatus, their nervous system, the position of the intestine, and even their 

 general form, are all of them circumstances in favour of their affinity with 

 Vermes." Cohn can find no true articulations, but merely shallow folds of 

 the skin in the principal portion of the body ; and even the pseudopodium 

 and toes are not articidated motory organs (or limbs), but prolongations from 

 the common cavity of the body. The circumstance of his having united the 

 Tardigrada with the Systolides (Rotatoria) indicates Dujardin's recognition 

 of the affinity of the latter with Crustacea ; for in structure the Tardigrada 

 make an unmistakeable approach to Arthropoda by the pairs of limbs and 

 chain of ganglions on the abdominal surface, and to Arachnida also by the 

 structure and disposition of their digestive organs, by their suctorial mouth, 

 and by other details of organization. Their association '\^dth Rotatoria, how- 

 ever, is not recognized by any other naturalist besides Dujardin ; and they 

 are generally placed amongst the lowest Arachnida, near the Pycnogonidce 

 and Acarhim (the lowest families of Arachnida) (see Section V., Of the Tar- 

 pigrada). 



A still higher affinity has been recently claimed for the Rotatoria by Mr. 



