§ 104. 



THE HELMINTHES. 



109 



a central nervous organ. There are, however, various other parts which 

 have been talcen for nerves, but some of these, certainly, do not belong to 

 this system. 



In the Cystici, no nervous system has yet been found, and the researches 

 made upon the Gestodes have ended equally unsatisfactory. A single 

 observation upon a Tetrarhyaais would lead us to thinlc that in these hist 

 the nervous system is situated at the cephalic extremity. 



In Tetrarhytichus attomatits, there is a small flattened swelling between 

 the sheaths of the four probosces, and from which pass off filaments to both 

 of these organs.'" 



The observations upon the nervous system of the Trematodes are more 

 numerous and positive. Immediately behind tlie oral sucker, and upon 

 the sides of the oesophagus, are two nervous swellings, connected by a 

 transverse cord, which passes beneath this canal. Among the branches 

 given off" in all directions from these, there are two, large and long, exteml- 

 ing from each side of the body to its extremity, and which give off in their 

 course many lateral branchlets.*'-' 



In Pentastoinuni, the central portion of this system consists of a single 

 large ganglion, sub-ossophageal, and due perhaps to the fusion of two lateral 

 ganglia. From this, filaments pass off in every direction ; two of these 

 surround the oesophagus in a ring-like manner, while two others, analogues 

 of the two main trunks of the Trematodes, pass to the very extremity of 

 the body, giving off on their way, very fine filaments.'^ 



1 Müller, not without reason, regards this organ 

 as the nervous system of Tetrarhynchus (Arcli. 

 1836, p. CVI.). New observations are needed to 

 decide if, as Lereboullet (Institut. 1839, No. 812, 

 p. lis) supposes, there can be included in this sys- 

 tem the two longitudinal stripes, which, with Ligu- 

 la simplicissiina, extend along both sides of the 

 ventral surface, and from which I, at least, have 

 seen pass no filaments.* 



'■i Our very e.xact knowledge of the nervous sys- 

 tem of Amphistomum subtriquetrum, and coni- 

 cum, and of Distomum hepaticum, we owe to the 

 researches of Bojanus (Isis 1821, p. 168, Taf. II. 

 fig. 11, 15, 19), of Laurer (De Amphistomo co- 

 nico, p. 12, fig. 21, 26), and of Mehlis (De Disto- 

 mate hepatico, p. 22, tig. 13). 



By continuing the methods of these helmintholo- 

 gists, this system wi^l undoubtedly be found in 

 otlier Trematodes. Diesiiig (Ann. d. Wiener Mus. 

 I. Abth. 2, p. 216, Taf. XXII. fig. 9) has found in 

 Amphistomum giganteum, and I have done the 

 same in Distomum daplicatum (wliich is prop- 

 erly only a larva of a species of this genus) the 

 same disposition noticed in Amphistomum coni- 



cum. In Distomum holostomum, I have found 

 also a similar structure, e.xcept that the two oesoph- 

 ageal ganglia are widely separated, aud united 

 by a very long cord-like commissure. Laurer 

 alone affirms to have seen enlargements upon the 

 principal nervous trunks of the Trematodes. But 

 their existence may be yet doul)tful for no other 

 anatomist has mentioned them, and in no case have 

 I myself been able to see them. 



3 Miram (Nov. Act. Acad. XVII. pt. 2, p. 632. 

 Tab. XLVI. fig. 8) did not, apparently, notice in 

 P'^ntastomum taenioides the nervous ring wliich 

 surrounds the tesopliagus ; although it had already 

 been noticed by Cuvier (R^gne Anim. III. 1830, 

 p. 251), and by Nordmann, in a work in common 

 with Mehlis (Microgr. Beitr. lift. 2, p. 141). The 

 existence of this ring has been placed beyond a 

 doubt by the figures of it as found in Pentasto- 

 mum taenioides, and proboscideum, given by 

 Owen (Trans, of the Zool. Sue. I. p. 325, PI. XI. 

 fig. 13, or Cyclop. Anat. and Phys. II. p. 130, fig. 

 78), and Diesing (Ann. d. Wiener Mus. I. Abth. 

 1, p. 13, Taf. I. II.).t 



* [ § 104, note 1.] Blanchard (Ann. d. Sc. Nat. 

 1848, X. p. 338) appears to have distinctly made 

 out a nervous system in Taenia. With Taenia 

 serrata, there are directly behind the proboscis two 

 small medullary nuclei united by a commissure ; 

 from these pass off on each side a nerve which is 

 distributed to the lateral parts of the head, and 

 connects with a ganglion situated at the base 

 of each sucker, which sends filaments to the 

 muscles of this last. Posteriorly there are given 

 off filaments which run parallel to the intestinal 

 tubes. This, however, has not been confirmed by 

 other observers, and Agassiz has made a statement 

 in a private letter to me which is worthy of notice. 



10 



He says : " I Irelieve the nervous system described 

 by Blanchard to be bands of muscular fibres which 

 cross each other between the fossae of the probos- 

 cis : at least, this is so in the new species of Taenia 

 from Amia ca/tio which was observed alive for sev- 

 eral hours ; and I could discover no nervous 

 threads, but only muscular fibres, which had ex- 

 actly the .".rrangement of Blanchard's nervous sys- 

 tem." See, however, falenciennes'' report to the 

 Acad, des Sc. in the Comp. Rend. 1847, XXIV. p. 

 1034, also Blanchard\s response to Dujardin, 

 Ibid. 1849, XXIX. p. 60. — Ed. 



t [ § 104, note 3.] Blanchard has found with 

 Linguatula another gaiighon above the cesopha- 



