38 THE NATUEAL HISTOET EEVIEW. 



BaglttcB must occupy a place among the Vermes, but their precise 

 position is still open to discussion. It is a question, however, 

 whether Dr. Carus might not have done better towards pro- 

 ducing a clear picture of this difficult branch of Zoology, had he 

 divided his Vermes only into three great classes, of which the first 

 might include the three groups to which we have already adverted. 

 The differences between his Annulata, Gephyrea, and Chsetognatha 

 are hardly of the value of those upon which classes of animals 

 are generally founded, and by including the constituents of the three 

 groups as orders of a single class, their stronger mutual affinity as 

 compared with that existing between them and the parasitic Nema- 

 telminthes and Platyelminthes would be better expressed. 



Of the former of these parasitic classes we need say but little, — 

 the author adopts the generally received classification of the Nema- 

 toid worms and follows Diesing for the most part in the subordinate 

 groups. But in regard to the Platyelminthes he reverts to the old, 

 and it seems to us erroneous, plan of including the Turbellaria 

 in the same class with the parasitic Trematode and Cestoid 

 worms, a proceeding from which we should have thought he 

 might have been restrained even by the difficulty which he has 

 evidently experienced in framing his definition of the class. The 

 Turbellaria are manifestly of a higher type than the Trematode 

 w^orms with which they are here associated, and approach in many 

 respects to the lower forms of the Hirudinea, most of which, like the 

 majority of the Turbellaria, are hermaphrodite. Moreover, in the 

 Turbellaria we find no trace of that complicated system of digenesis 

 which prevails, as far as we know, almost throughout the Trematode 

 and Cestoid worms, — the so-called alternation of generations in the 

 Nemertiua being of a very dissimilar nature. 



The classification of the Turbellaria here adopted is founded upon 

 the systems proposed by Keferstein, Max Schultze, and Schmarda, 

 with the introduction of some groups established by Mr. Stimpson in 

 his " Prodromus," published in the Proceedings of the Philadelphian 

 Academy for 1857. The Trematoda and Cestodea are arranged 

 in accordance with the latest systematic views of Van Beneden. 



It is unfortunate with respect to furnishing the student with a 

 clear view of the primary grouping of the animal kingdom, that the 

 five main sections described in this volume are represented tyjpo- 

 grapliically as of equal value, although three of them are regarded by 

 the authors as going to make up the great division of the Annulosa, 



