or THE NEMATOIDS, PAEASITIC AND FREE. 551 



This I have seen most plainly in individuals from the stomach of a hare (Plate XXVII. 

 fig. 10), though I have recognized a similar arrangement less distinctly in S.filaria and 

 S. auricularis. In Trichocephalus affinu, in place of the two layers with oblique inter- 

 secting lines, there is a single layer with transverse lines of a similar character, though 

 quite different from the more pronounced markings of the surface layer. In a species of 

 Mlaria examined, I could detect only a thin external layer with transverse markings, 

 and a thick structureless portion, apparently devoid of markings, intervening between it 

 and the very thin cellular layer ; whilst in Prosthecosacter inflexus only one structureless 

 and very transparent glass-like epidermic layer exists, which being developed into ridges 

 in an irregular manner upon its surface, causes it to exhibit a similar arrangement of 

 lines or in tegumental markings when seen by transmitted light (Plate XXVII. figs. 4 & 7). 

 In this animal also the deep skin layer is remarkably thin. 



The integument of the free Nematoids is evidently formed upon the same type, but I 

 have distinctly recognized oblique intersecting lines in the internal layers of Borylaimus 

 stagnalis only. Dujardix has also represented these. In this animal there are no 

 transverse markings of the external layer, but well-marked longitudinal ones. The 

 representatives of other genera, such as Enoplus and Chromadora, present both transverse 

 and longitudinal lines, the former being most pronounced in the genus Chromadora and 

 the latter in Enoplus; whilst in Plectus, Trilobus, and many other genera transverse 

 markings only are seen. 



In the genera Cyatholaimus and Spilophora we meet with circular rows of dots instead 

 of lines, and in several genera, such as Leptosomatum, Phanoderma, &c., no integumental 

 markings whatever can be recognized. The cellular enderon I have not detected in 

 these animals*, except as it exists in the lateral regions of the body, where it constitutes 

 the lateral bands. These animals are so small that the difficulty of making satisfactory 

 transverse sections has hitherto been insuperable. 



In both the parasitic and the free Nematoids the chitinous portion of the integument 

 is occasionally developed into alae or other projections ; these are cervical in Ascaria 

 mystax, and principally composed of a development of what is generally the thickest 

 layer, viz., the second from without inwards. But these developments more commonly 

 exist as caudal expansions in the male, such as are so well known in the genera Stron- 

 gylus and Spiroptera amongst the parasitic species. Structures of a similar nature may 

 be seen amongst the free Nematoids in tlie genus Shabditis, where the lateral alae are 

 supported by sets of delicate raysf, and in Tylenchus, where they are less developed and 

 unsupported by such processes^. 



The development of the external layers of the integument into spines is not an 

 unfrequent occurrence amongst the parasitic Nematoids; these are somewhat conical, 



* Unless, as seems most probable, the almost superficial cells met with in many species of the genus Cyatho- 

 Immus (Plate XXVIII. fig. 36), giving them their characteristic maculated appearance, do in reality belong to 

 this layer. 



t Trans, of Linn. Soc. vol. xxv. pi. 10, fig. 62. J Ibid. pi. 10, fig. 114. 



