596 DR. H. CHAELTON BASTIAN ON THE ANATOMY AND PHYSIOLOGY 



Nothing that can be called a lateral band is met with in Dracunculus medinensis. In 

 this animal, it is true, an unusually wide intermuscular space exists (Plate XXV. fig. 14), 

 covered by a thin stratum of the deep cellular integumental layer ; and though no pro- 

 minence whatever can be observed, we must undoubtedly look upon this portion of the 

 granulo-cellular layer lining the chitinous external integument, as the undeveloped 

 homologue of what, in most Nematoids, constitutes the lateral band. We see in this 

 stratum, thin as it is, the characteristic nucleated cells*, and running along its median 

 line a most delicate vessel only oinro" ^^ diameter. What is the nature of the peculiar 

 ganglionated cord (in the same position and in contact with the longitudinal vessel) 

 which I formerly described as a nerve, I am now quite imable to understand f. I have 

 been able to ascertain nothing concerning it by means of transverse sections, except 

 that it seems to constitute a fiat band whose situation is not even marked by a thickening 

 of the cellular layer in the middle of the intermuscular space. The anterior and pos- 

 terior terminations of these bodies, as well as of the longitudinal vessels, is still unknown, 

 and must be made the subject of future investigation. 



The median lines have been frequently mentioned incidentally, so that I have now 

 little to add concerning them. As before stated, they do not always exist, but when 

 present I believe their method of formation and stnicture to be similar to that of the 

 lateral lines. I therefore look upon them also as developments of the deep layer of the 

 integument. They are usually small and narrow, in accordance with the nature of the 

 intermuscular interval in the mid-dorsal and mid-ventral regions ; but, as we have already 

 seen in certain species of the genus Trichosoma, the dorsal or ventral bands may much 

 exceed the lateral in width, and a study of these animals alone is sufficient to support 

 the opinion of the absolute identity, as regards histological structure, of the lateral and 

 median bands in the Nematoids — an opinion, however, which I had held long before I 

 was aware of the additional proof afforded by the interchangeable nature of these 

 structures amongst the Trichosomata. Accessory median lines, one on each side of the 

 primaiy, exist in many of these animals, and the same arrangement appears to prevail 

 in Prosthecosacter injlexus (Plate XXVII. fig. 4, b', V). In this animal they form the 

 narrowest possible prolongations up between the muscular bundles, and are principally 

 recognizable when the body of the animal is slit open and the internal organs removed, 

 by the slight swellings which appear in their course, at intervals, along the surface of the 

 longitudinal muscles. The ordinary single median line in the dorsal and ventral region 

 may be best studied in Ascaris lumbricoides and A. megalocephala, and in Spiroptera 

 obtusa. They seem to me absent altogether in A. osculata, Ciicullanus heterochrous, 

 and a species of Filaria which I have examined, whilst Eberth has also faUed to recog- 

 nize them in Strongylus tenuis and Sclerostomum dentatum. They very likely exist in 



* Vide Trans, of Linn. Soc. vol. xxiv. pi. 21. fig. 25. 



t When I formerly made this statement I did not know so much concerning Nematoid Anatomy, and although 

 I never felt quite satisfied about its histological resemblance to a real ganglionated nervous cord, I at the time 

 xlescribed it as such simply by way of exclusion — there seemed to be nothing else which it could possibly be. 



