§ 104. 



THE HELMINTHES. 



109 



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

 have been taken 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 Cestodes have ended equally unsatisfactory. A single 

 observation upon a Tetrarhyncus would lead us to think that in these last 

 the nervous system is situated at the cephalic extremity. 



In Tetrarhyyichus attenuatus, 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 the oral sucker, and upon 

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

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

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

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

 course many lateral branchlets.*-' 



In Pentastomum, the central portion of this sygtem consists of a single 

 large ganglion, sub-oesophageal, 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 wa}^, very fine filaments.^ 



1 Mailer, not without reason, regards this organ 

 as the nervous system of T etrarhynchus (Arch. 

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

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

 p. 118) supposes, there can be included in this sys- 

 tem the two longitudinal stripes, which, with Ligu- 

 la simplicissbna, extend along both sides of the 

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

 seen pass no filaments.* 



2 Our very exact knowledge of the nervous sys- 

 tem of Amphistotnum subtriqtietrum, and coni- 

 cum, and of Distomum hepatictim, we owe to the 

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

 fig. 14, 15, 19), of Laurer (fie 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 will undoubtedly be found in 

 other Trematodes. Dicsinv (Ann. d. Wiyner Mus. 

 I. Abth. 2, p. 246, Taf. XXII. fig. 9) has found in 

 Amphistornum ^i^anteum, and I have done the 

 same in Distomum dupUcatum (which is prop- 

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

 same disposition noticed in Amphistornum. coni- 



cum,. In Distomum holostomum, I have found 

 also a similar structure, except that the two oesoph- 

 ageal ganglia are widely separated, and 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 doubtful 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 

 Pentastomum, taenioides the nervous ring wluch 

 surrounds the oesophagus ; although it had already 

 been noticed by Cuvier (R6gne Anim. III. 1830, 

 p. 254), and by Nordmann, in a work in common 

 with Meklis (Microgr. Beitr. Hft. 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. Soc. I. p. 325, PI. XI. 

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

 IS), 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 



lie says : " I believe the nei-vons 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 .4m ja caZro which was observed alive for sev- 

 eral hours ; and I could discover no nervous 

 threads, but only muscular fibres, which had ex- 

 actly the arrangement of Blanchard''s nervous sys- 

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

 Acad, des So. m the Comp. Rend. 1847, XXIV. p. 

 1034, also Blanchard's response to Dujardin, 

 Ibid. 1849, XXIX. p. GO. — Ed. 



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

 Linguatula another gangUou above the oesopha- 



