OF THE NEMATOIDS, PAEASITIC AOT) FEEE. 571 



amiatus. I have also detected the oesophageal band and ganglion-cells in Ascaris 

 marginata, A. osculata, A. spiculigera, A. mystax, and Dracunculus medinerms, and 

 have seen, from the exterior only, what seemed undoubtedly the oesophageal band in 

 Strongylm Jilaria and Cucullanus heterockrous. 



Leuckart has described a pale nervous band containing ganglion-cells surrounding 

 the oesophagus, close behind the mouth, in Oxyuris vermicularis, and has also described * 

 what he considers to be a nervous ring, occupying a similar situation, in Trichocephalus 

 hominis and Trichina spiralis. Eberth f has likewise seen a structure of the same kind 

 in several Trichocephali and Trichosomata, though he seems very unwilling to look upon 

 it as constituting part of a nervous system. 



As to the peculiar, bright, homogeneous-looking ring surrounding the oesophagus in 

 some parasitic Nematoids, such as Eberth has figured ;|; in Spiroptera megastoma and 

 Sderostomum dentatum, there can, I think, be little doubt that this is homologous with 

 the similar body surrounding the oesophagus of so many of the larger marine Nema- 

 toids, and concerning which both Eberth and myself have already expressed our opinions 

 that it does not belong in any way to the nervous system. It differs altogether from the 

 nervous oesophageal band now distinctly recognized in so many Nematoids, not only by 

 its position, which is often far removed from the mouth, but also by its structure and 

 disposition. No fibres can be recognized in its tissue, it is considerably larger and 

 thicker in size, and, in addition, seems to be connected more intimately with the 

 oesophagus itself than with the parietes of the body. 



Notwithstanding the existence of well-developed ocelli in many species of free Nema- 

 toids, both Eberth and myself have been quite imable to detect any nerve-filaments in 

 connexion with them, or in fact any certain evidence of the presence of a nervous 

 system in these animals. That such a system does exist I have not the smallest doubt ; 

 and considering the difficulties besetting its recognition even in large species of parasitic 

 Nematoids, I think that our failure hitherto in demonstrating its existence in these com- 

 paratively minute animals is after all, notwithstanding their transparency, no very great 

 cause for wonder. 



I have lately, in examining some of these animals with a -^5" object-glass, detected 

 some almost invisible fibres surrounding the oesophagus. I have recognized them 

 distinctly in Monhystera stagnalis and in Plectus parietinus. In this last species they are 

 situated, too, just anterior to the orifice of the ventral gland. I think it very probable 

 that this may be its nervous oesophageal band, but cannot speak more positively on the 

 subject. 



* Bericht uber der Leistungen in der Naturgeschichte der niederen Thiere fiir 1859, und Untersuch. iiber 

 2VtcA. spiralis, S. 48. 

 t Untersuch. iiber Nemat. S. 51. :[: Loe. cit, Taf. ix. 



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