Minot.] 24 [November 15, 



The classification of the Plathelminths therefore assumes the fol- 

 lowing form : — 



Accela, ~] 



Apharyngea f Rtebdoccela. 



Pharyxgoccela, j 



Khabdoccela, J 



Dendroccela, Dendroccela. 



VAGDSTIFERiE, 



Trematods, Trematods. 



Cestods, Cestods. 



Besides these forms, Microstomum and the Gastrotricha have been 

 classed together with Turbellarians. The former have hardly been 

 studied anatomically yet. It is, on the other hand, probable that the 

 latter are really related to the Apharyngea. In this case the Plat- 

 helminths would be brought into relation with Butschli's new group, 

 the Nematorliyncha. 1 



If the Plathelminths were, on the other hand, related directly to 

 the higher worms, we should expect to find some points of close 

 resemblance in structure, which however we do not. The affinity 

 formerly supposed to exist between them and the leeches has been 

 found, upon more accurate investigation, not to be genuine. It 

 appears to me very probable that our class may be related to the 

 Nudibranchs. I hope to be able to investigate this point shortly, and 

 will not therefore discuss what is at present a mere hypothesis. 



1 have finally to state that the investigations, the general results of 

 which I have here communicated, were made in the laboratories of 

 Profs. Semper and Leuckart, to whose invaluable assistance much of 

 the worth these studies may have must be attributed. I must thank 

 them warmly for their help. The extended memoir will, I hope, be 

 published before long in. Prof. Semper' s Arbeiten des Zootomisch- 

 zoologischen Instituts zu Wurzburg. 



Note. Since writing the above, I have received Professor Sem- 

 per's very important and interesting memoir 2 on the homologies 

 existing between worms, vertebrates and arthropods. He has 

 opened a vast field of new discoveries, and discusses the relationship 



1 Biitscbli. Untersuchungen iiber freilebende Nematoden und die Qattung Chae- 

 tonotus. Zeit. wiss. Zool., xxvi (1875-76), p. 392. 



2 Semper. Die Verwandtscbaftsbeziebungen der gegliederten Tbiere. in, 

 Strobilation und Segmentation. Ein Versuch zur Feststellung specieller Homolo- 

 gien zwischen Vertebraten, Anneliden und Artbropoden. Arbeit. Zool. Inst. 

 Wurzburg, Bd. in, p. 115 (1876). 



