108 §$ 104. 
THE HELMINTHES. 
of the last row are only rudimentary. The sheath of the proboscis is very 
muscular, and terminates behind in a caecum; it extends across the neck of 
the animal even into the cavity of the body, and its movements are aided by 
some special muscles. In all the species whatever, there are three muscles 
which act as retractors of the sheath and neck. Two of these arise as 
delicate cords at the anterior extremity of the body from both sides of the 
internal surface of the subcutaneous muscular sac; they traverse thence 
the cavity of the body obliquely, and are inserted,in Echinorhynchus acus, 
angustatus, fusiformis, and proteus, upon the sides of the sheath; but in 
Echinorhynchus gigas, haeruca, polymorphus, hystrix, and strumosus, the 
insertion is at its inferior extremity. Between these two muscles, and 
below their points of origin, there is a third, which divides from the sub- 
cutaneous muscular sac; this is simple, riband-like, and is inserted at the 
lower extremity of the sheath. In Echinorhynchus polymorphus, and pro- 
teus, its form is pyramidal. In Echinorhynchus gigas, and gibbosus, two 
thin muscles arise from the anterior extremity of the body, and are inserted 
‘upon the sides of the sheath; they serve, probably, for the protrusion of 
this organ and the neck. 
There are, moreover, upon the different parts of the body of some Hel- 
minthes, horny hooks and spines, which serve for their creeping about and 
permanent attachment to objects. 
CHAPTER III. 
NERVOUS SYSTEM. 
§ 104. 
The apparently quite feebly-developed nervous system of the Helminthes 
is yet but very incompletely known. 
Our whole knowledge is limited to that of a small obscure ganglion found 
in some species, which, as it sends off several nerves, may be regarded as 
6 Helminthologists are not yet agreed as to the 
a sting which projects from the back above the 
ber and arra of the pr ideal mus~ 
oral sucker (and not from the mouth itself, as Wag- 
cles of the Acanthocephali ; see Vitzsch, in Ersch 
and Gruber’s Encyclop. I. 1818, p. 242; Bojanus, 
in Isis, 1821, Taf. III. fig. 34; Westrumb, De 
Helminthibus Acanthocephalis 1821, p. 50; and 
Cloquet, Anat. des Vers. intestin. p. 76, Pl. VII. 
Mehlis (Isis 1831, p. 82) has taken the probosci-~ 
deal sheath for an cesophageal organ, and its two 
muscles for vessels. Burow (Echinorhynchi stru- 
mosi Anatome, 1836, p. 16, fig. 1, e) has fallen 
into a similar error, in regarding these same mus- 
cles as intestinal tubes. 
7 With many Tr des, as, for e le, with 
Polystomum, Octobothrium, &c. (see Baer, Nov. 
Act. Acad. Leop. Carol. XIII. pt. 2, Tab, XXXII. 
fig. 7, f. and Mayer, Beitrage, &c., Taf. III. fig. 
3, m. m. fig. 8), there are found between the suck- 
ers at the posterior extremity, special hooks, and 
to which, with Polystomum, I have seen proper 
muscles proceed from the interior of the body. 
With certain Cercariae(larve of Distomum) one 
‘an distinctly observe the use which they make of 
ner has supposed, Isis. 1834, p. 131), and which 
serves to open a passage through the parenchyma 
of the animals they infest. An entire group of 
Distomum, as Distomum echinatum, militare, 
uncinatum (Bremser, Icon. Helminth, Tab. X. 
fig. 5), which Rudolphi has designated as Echinos- 
tomata, have around their oral sucker an annular 
collar, upon which are numerous straight spines 
arranged in a circular manner. An armature of 
this kind is found upon a Cercaria. These spines 
are as easily detached as the hooks of the armed 
Taeniae. With Spiroptera crassicauda, I have 
found on each side of the mouth a doubly-pointed 
sting pointing backwards, and behind this two 
others three-pointed. A still more remarkable 
form is seen in the four penniform stings, which 
project behind the mouth of Ancyracanthus 
pinnatifidis (see Diesing, Aun. d. Wiener Mus. 
IL. Abth. 2, Taf. XIV. XVII1.). These Nematodes 
undoubtedly use these instruments for piercing the 
stomachal membranes of the animals they infest. 
