OF THE NEMATOLDS, PARASITIC AND FEEE. 647 



modified, and the nature of the alterations encountered tends only to ally them more 

 closely by organization as well as habitat to the members of the class Echinodermata. 



The remarkable tenacity of life, and power of resuming all their vital manifestations 

 after the most prolonged period of desiccation and torpidity, possessed by some of the 

 free Nematoids, in common with the Rotifera, make them objects of extreme interest 

 to the biologist, which interest, certainly, suffers no diminution from the fact that, so far 

 as I have observed, this extraordinary attribute is possessed only by members of the four 

 land and freshwater genera, Tylenclms, Aphelenchtis, Plectus, and Cephalohus, whilst other 

 representatives of the family are frail, and unable to recover even after the shortest 

 periods of desiccation. 



My observations on the anatomy of the parasitic Nematoids have been conducted 

 more or less fully upon twenty-six species, some of which belong to each of the seven 

 sections into which Dujardin* divided the order, though I have studied most completely 

 seven species of the genus Ascaris, and of these especially Ascaris lumbricoides and 

 A. megalocephala. In many important particulars these observations are in accordance 

 with the results of the recent researches of Drs. Schneider and Ebeeth in Germany, 

 whose investigations have done so much to improve the state of our knowledge con- 

 cerning the organization of these animals ; though, as will be seen under the various 

 subdivisions, there are many other points upon which I have been unable to reconcile 

 my observations with those of either one or both of these anatomists. Although, 

 therefore, difficulties and some disagreements still remain, yet I hope to be able to 

 remove many which have hitherto obscured this subject, and to offer suggestions which, 

 if accepted, will go far to solve the question of the zoological affinities of the Nematoids. 



TEGUMENTARY ORGANS AND APPENDAGES. 



Many misconceptions have prevailed concerning the nature of the integument in the 

 Nematoids, as I .have already pointed out in the paper " On the Structure and Nature 

 of the Dracunculus"^. It has been described by Von Siebold:|:, Dujabdin§, Owen||, 

 and most other anatomists, as divisible into two main portions — a structureless epi- 

 dermis composed of chitine, and a corium made up of layers of longitudinal and oblique 

 decussating fibres. And, although in this communication I pointed out the fact that 

 these so-called fibrous layers, or membranes, were not such in reality, but that, in 

 common with the external more homogeneous layer, they were essentially epidermic in 

 nature, consisting of chitinous lamellae presenting various kinds of markings, and, in all 

 probability, were excreted from some deep cellular layer, still, I had not at that time 

 been able actually to recognize the existence of such a layer in the Nematoids. Since 

 then I have fully satisfied myself of the existence of a distinct, deep, cellulo-granular 



• Histoire Natuxelle dcs Hclminthes, 1845, p. 2. 



t Trans, of Linn. Soc. vol. xxiv. p. 108. J Manuel d'Anat. Comp. Trad. Fran5aise, 1850, p. 115. 



§ Hist. Nat. des Helminthes, 1845. || Lect. on Comp. Anat. 2nd edit. 1855, p. 99. 



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