620 DE. II. CHAELTON BA8TIAN ON TIIE ANATOMY AND PHYSIOLOGY 



also capable of resisting the effects of many other agents which would speedily prove 

 fatal to others of their kindred not similarly endowed. There seems to be some innate, 

 though inscrutable difference in the intimate constitution of their tissues, into the nature 

 of which we may never be enabled to penetrate, even with the most perfect instrument 

 the optician could devise. 



ZOOLOGICAL POSITION AND AFFINITIES. 



Having noAV pretty fully explained the anatomy of the Nematoids, we shall be able, 

 with the aid of the many new facts revealed concerning their structure, to consider the 

 question of their affinities and homologies with more chance of success than formerly, 

 so that we may hope to throw some light upon this difficult subject. Hitherto, to 

 those anatomists who penetrate beyond mere external form, the Nematoids have been 

 regarded almost as an outlying group, having no definite relationship with other 

 animals, and admitting only of a provisional location in the convenient though 

 utterly artificial class Entozoa. In the first volume of his ' Elements of Comparative 

 Anatomy' recently published. Professor Huxley has done much to elucidate the 

 homologies of the "Annuloid" animals; and as well from the philosophic nature of 

 his views as from the fact that he is the latest writer of note who has treated on the 

 classification of the Animal Kingdom, it seems desirable for me briefly to refer to some 

 of these views in order that we may be able more fully to appreciate the state of the 

 question concerning the affinities of the Nematoids. 



In his ' Lectures on General Natural History' * he divided the subkingdom Annulosa 

 into two great divisions, the Aeticulata or Artheopoda and the Annuloida ; including 

 in the former division Insecta, Myriapoda, Crustacea, and Araclmida, whilst in the 

 latter he placed Annelida, EcJiinodermata, and Scolecida — the latter being a name under 

 which he still proposes to include the Entozoa, TurheUarice, and Botiferce. 



In the recently published workf , however, this classification is somewhat modified ; 

 since whilst acknoAvledging that " the members of the class Annelida present marked 

 differences from all the Arthropoda, but resemble them in one important particular, and 

 that is the arrangement of the nervous system, which constitutes a ganglionated double 

 chain traversed at one point by the oesophagus," still he now thinks " that the resem- 

 blances between the Annelida and Arthropoda outweigh the differences, and that the 

 characters of the nervous system and the frequently segmented body, with imperfect 

 lateral appendages of the former, necessitate their assemblage with the Arthropoda into 

 one great division or subkingdom of Annulosa." 



Whilst laying little stress now upon the few resemblances of the Echinoderms and 

 Scolecids to the Annelids, such as the occasional resemblance between their ciliated 

 larvse, and the possibility of the vessels of the Annelids being modified representatives 

 of the water-vascular apparatus, he thinks there can be no doubt as to the many singular 

 resemblances which unite the Scolecids and the Echinoderms together. And whilst 

 • Med. Times, 1856, ii. p. 27. t On the Elements of Comp. Anat. 1864, p. 75. 



