298 NEMATHELMINTHES. 



Following the usual custom, the Acanthocephala are placed in 

 the phylum Nemathelminthes ; but it must be borne in mind that 

 the relationship to the Nematoda thus expressed is more than 

 doubtful. Indeed, there is nothing in common between the two 

 groups, and there are many remarkable differences. The absence 

 of an alimentary canal, the presence of a coelorn with relations to 

 the generative organs and ducts, the form of the nervous system, 

 the presence of cilia in the so-called nephridia, are all characters 

 of great importance and quite different from anything in the 

 Nematoda. Further, the canals in the skin, though they may 

 be compared to the lateral excretory organs of Nematodes, are, in 

 reality, totally different, inasmuch as they form anastomosing net- 

 works, and are found throughout the whole of the epidermis. 

 Finally, the development cannot be brought into relation with 

 anything else in the animal kingdom. It is peculiar in the fact 

 of the giant nuclei of the outer layer and in their behaviour, and 

 in the absence of a third layer or group of cells in the early stages. 



Our inclination is to create a separate phylum the Acantho- 

 cephala for this strange group of parasites. 



