ON THE STRUCTURE OF THE ROTIFERA. 137 



We have also appended the author's Systematic arrangement 

 of the Rotifera, 



ON THE SYSTEMATIC POSITION OF THE EOTIFEKA. 



Formerly placed among tlie Infusoria, of which they formed the second 

 class in the classification of Ehrenberg, it has been latterly admitted by 

 all systematic writers, that the Rotifera possess nothing in common 

 with the animals truly belonging to tliat class, or the polygastrica of the 

 Berlin Professor : but that, in respect of their complex structure, they 

 represent a higher type of organization. Opinions, however, are still 

 divided on the question, whetlier the Botifera, as Burmeister believes, 

 belong to the Crustacea, or should be referred to the Annelids, in accord- 

 ance with the opinion of Wiegmann, Wagner, Milne-Edwards, Berthold, 

 V. Siebold, and others. 



If the truth were always with the majority, we should undoubtedly be 

 obliged to place the Rotifera in the class of Annelida ; but I believe, 

 nevertheless, that Burmeister is in the right, though opposed to all the 

 other observers above named. / also conceive that the Rotifera are much 

 ■more closely allied to the Crustacea than to the worms ; and, by comparing 

 the conditions of organization of the two classes, shall venture to support 

 this view in the following observations. 



It may first be mentioned, that so far back as 1824 Nitzsch asserted, 

 that the Rotifera resembled the Entromostraca ; and, what certainly 

 deserves attention, Ehrenberg himself, though placing them with the 

 Infusoria, frequently remarks upon their resemblance to the Crustacea 

 and Entomostraca ; thus, in his great work, p. 410, he says, that the 

 " spicules, beards, and setaj" of many species might be compared with the 

 arms of the Daphnice ; and in p. 411 he remarks, that many Rotifera carry 

 about their eggs attached to them, " like the Crustacea ;" and speaks to 

 the same effect in many other places. Dujardin also notices similar resem- 

 blances with Cyclops, Cypris, &c. ; as, for instance, at pp. 574 and 575 

 of his work. 



If the systematic position of the Rotifera were to be determined mainly 

 from their external fiyure, the result would certainly be more in favour of 

 the Crustacean than of the Annelid^type. No annelid has articulated motile 

 organs, whilst, on the contrary, the possession of such organs in a per- 

 fectly symmetrical form is a fundamental character of the Arthropoda. 

 The majority of the Rotifera are not furnished, it is true, with a jjair of 

 feet, although they have a single annulated, or jointed foot, containing no 

 part of the viscera, but which is applied solely to the purpose of loco- 

 motion. Furthermore, if the rest of the conformation of the body be 

 regarded, it is obvious at once that a Euchlanis, Salpina, and, in short, 

 all whose cuticle has acquired the hardness of a lorica, are more closely 

 approximated to a crustacean than to a worm. For in the whole vermi- 

 form division I am unacquainted with any form whose cuticle is indurated 

 to the same extent. 



The muscular structure also approximates, in many Rotifera, more 

 nearly to the Arthropoda than to the Annelids. In no animal of the 

 latter class have genuine transversely striped muscles hitherto been seen ; 

 that is to say, muscles whose contents are divided into minute quadran- 

 gular particles, like those of the muscles of vertebrate animals. 



That the motions of the body of many species recall in a striking 

 manner those of the Crustaceans has already been noticed. 



If the nervous system be considered, its similarity with that of the 



