AND THE CLASSIFICATION OF WORMS. -q 



_ In two papers, cited at the head of this article, I have already considered the striking 

 similarity existing between the flukes and the tape worms in their adult forms The 

 examination of Distomum crassicolle has confirmed my views ; but it is not yet pos- 

 sible to perfectly homologize the water- vascular system in the two orders, nor to explain 

 the absence of the nervous system and the digestive canal in the Cestods. In all other 

 respects there is an essential agreement; but the developmental history, accompanied in 

 one order by a different alternation of generations from that occuring in the other, must 



doubi e uniou ° f the two divisions can be settled bejond a11 p° ssibilit y of 



Prof Huxley Mias recently proposed some alterations in zoological classification, appar- 

 ently taking Haeckel s gastraea theory as a starting point. He is thereby led to surest 

 various changes in the classification of the worms, which result in an arrangementTery 

 different from that which seems to me most near the truth. 



I cannot but consider it very unfortunate that Prof. Huxley has so entirely accepted the 

 gastnea theory, for it has been very severely condemned by various competent naturalists, 

 and it w not, so far as I am aware, generally adopted. Sufficient condemnation of the 

 theory that the primitive germinal layers are really homologous in the ways expounded 

 by Haeckel is found in the fact that the layers arise by processes apparently altogether dif- 

 ferent in different animals ; for it is the established law that those parts are the same which 

 are formed in the same manner. That the germinal layers are homologous, few natural- 

 ists now doubt j but that the Gastrula is the primitive form has been as urgently denied by 

 some embryologists as affirmed by others. Under these circumstances it seems to me pre- 

 mature to recast the whole of zoological classification in accordance with the demands of 

 the " Gastrceatheorie." 



I am not surprised, therefore, that Prof. Huxley's results are very discordant with those 

 of other naturalists as to the classification of the worms. Huxley, taking into considera- 

 tion that the adult tape worms have no digestive canal, as do their allies, suggests separat- 

 ing them from the other Plathelminths, and joining them with the Acanthocephala under 

 the name of Agastraea. I believe that there is not a single close homology yet demon- 

 strated between the Echinorhynchi and the Cestods, while, on the other hand, it has long 

 been known that the Cestods were related to Trematoda and Turbellaria, and I have only 

 endeavored to show that the relationship is even much closer than had been supposed. I 

 am not aware that Huxley has brought forward any new arguments which prove the im- 

 possibility of maintaining the order of the Vaginiferse. 



Prof. Huxley has further divided the class Annelida, separating the Oligochseta from the 

 PolychaBta, upon what appear to me very insufficient grounds. What especially concerns 

 us here is the approximation of the annelidan leeches and the Trematods; in favor of this 

 union I am not acquainted with a single argument, and therefore it appears unnecessary to 

 discuss it further, for I hold it for a well established truth that the leeches are annelids and 

 have no immediate connection with the Plathelminths. 



t 



1 Huxley. On the Classification of the Animal Kingdom. Journ. Linn. Soc, Lond., Vol. xn, p. 199. 



