$ 104. THE HELMINTHES. 109 
@ 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 Tetrarhynchus 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 esophagus, 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, 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 system consists of a single 
large ganglion, sub-cesophageal, and due perhaps to the fusion of two lateral 
ganglia. From this, filaments pass off in every direction; two of these 
surround the cesophagus 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 Miller, not without reason, regards this organ 
as the nervous system of T'etrarhynchus (Arch. 
1836, p. ay 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 simplicissima, 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 Amphistomum subtriquetrum, and coni- 
cum, and of Distomum hepaticum, we owe to the 
researches of Bojanus (Isis 1821, p. 168, Taf. IT. 
fig. 14, 15, 19), of Laurer (De Amphistomo co- 
nico, p. 12, fig. 21, 26), and of Mehlis (De Disto- 
mate heputico, p. 22, fig. 13). 
By inuing the methods of these hel 
gists, this system will undoubtedly be found in 
other Trematodes. Diesing (Ann. d. Wiener Mus. 
I. Abth. 2, p. 246, Taf. XXII. fig. 9) has found in 
Amphistomum giganteum, and I have done the 
same in Distomum. duplicatum (which is prop- 
erly only a larva of a species of this genus) the 
same disposition noticed in Amphistomum coni- 
hol 
* [§ 104, note 1.) Blanchard (Ann. d. Sc. Nat. 
1848, X. p. 3388) 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 
cum. ln Distomum holostomum, I have found 
also a similar structure, except that the two cesoph- 
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, hotice in 
Pentastomum taeniotdes the nervous ring which 
surrounds the cesophagus ; although it had already 
been noticed by Cuvier (Régne Anim. ILI. 1880, 
p. 254), and by Nordmann, in a work in common 
with Mehdis (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 t iotdes, and prob di > given by 
Owen (Trans. of the Zool. Soc. I. p. 325, Pl. XL 
fig. 18, or Cyclop. Anat. and Phys. II. p. 130, fig. 
78), and Diesing (Ann. d. Wiener Mus. I. Abth. 
1, p. 18, Taf. L. I1.).t 
He says: ‘I believe 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 calva which was observed alive for sevy- 
eral hours; and I could discover no nervous 
threads, but only muscular fibres, which had ex- 
actly the srrangement of Blanchard’s nervous sys- 
tem.” See, however, Valenciennes’ 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.— Ep. 
t [§ 104, note 3.} Blanchard has found with 
Linguatula ano*her ganglion above the cesopha- 
