$ 103. THE HELMINTHES. 107 
The young of Echinococcus, Coenurus, Cysticercus, and many of the 
Taenia, have their head armed with a circle of single or double hooks, 
which were known to the oldest Helminthologists. Each hook consists of 
a, strongly-curved point, situated upon a round, straight pedicle, of varia- 
ble length. At the point where the curve ceases, there is, upon the con- 
cave side of the organ, a small conical process. When this circle of hooks 
is unfolded, the points project around the anterior part of the head, whilst 
the pedicles point towards the inner and their processes towards the poste- 
rior portion of the body, and are buried in the parenchyma. Both are 
surrounded by muscular substance. When, therefore, the muscles of the 
pedicles contract, the hooks are drawn downwards and outwards, and their 
points are brought together upon their convex surface in the long axis of 
the head; but when, on the other hand, the muscles of the processes con- 
tract, these last are depressed, the pedicles are again elevated, and the 
hooks project outward. With many Cestodes, this circle of hooks is situ- 
ated upon a particular proboscis (rostellum), which can be retracted into a 
sheath which is concealed between the four suckers of the head. 
With Anthocephalus, Gymnorhynchus, and Tetrarhynchus, there are 
upon the head four long and completely retractile probosces, which are 
armed with an extraordinary number of small, backwardly-curved hooks 
which are attached by a large base to the external surface of the organ, 
and are without special muscles; by these, these animals can penetrate the 
most compact animal tissues. Hach proboscis is a hollow muscular tube, 
which can be voluntarily retracted within a sheath of the same nature, and 
then the hooks, with their points directed in front, are drawn together in 
its axis. 
depends upon that of the proboscis. 
The length of the sheath, which is usually enlarged at its base, 
In many species of Tetrarhynchus, 
they reach far into the neck of the animal. 
The Acanthocephali have only one of these organs, and the hooks, which 
are without special muscles, form rows arranged one after another. 
Both 
the number of these rows and the form of the hooks vary in different 
species. 
the suctorial apparatus of the Trematodes. In T'ris- 
tomum hamatum (see Rathké, Nov. Act. Acad. 
Leop. Carol. XX. 1843, p. 241, Taf XII. fig. 11), 
several sharp points project from the bottom of the 
sucker at the posterior extremity. With Polysto- 
mum appendiculatum (Nordmann, Micrograph. 
Beitrage, Hft. I. p. 82, Taf. V. fig. 6, 7), the borders 
of the six suckers at the posterior extremity are 
armed with a sharp claw. The disc of Gyrodac- 
tylus (Ibid. Taf. X.) has its borders provided with 
six horny points, and its base is supported by two 
sides of the same nature, curved like an arc. 
A very complicated support, formed of horny 
arches and ridges, sustains the eight suckers at the 
posterior extremity of Octobothrium sagittatum, 
Merlangi, and of Diplozoon paradorum; an 
analogous support wholly surrounds the large foot 
at the end of the body of Avine (Leuckart, Zool. 
Bruchstiicke Hft. 3, Taf. II. and Nordmann, 
Micogr. Beitr. Hft. 1, Taf. VIL.; also Diesing, 
Nov. Act. Acad. Leop. Carol. XVIII. pt. 1, Tab. 
XVII). 
The four fossae found on each side of the mouth 
of Pentastomum contain simple and double very 
curved hooks, which the animal can erect at will 
brenine Ann. d. Wiener Mus. I. Abth. 1, Taf. 
A remarkable exception among the 
Nematodes is found with Hedruris androphora, 
. IV). 
Usually their size decreases from before backwards, so that those 
of which Nitzsch (Ersch and Gruber’s Encyclo- 
ped. VI. p. 49, [X. Taf. II. A.) has made a sep- 
arate genus ; the females have a protrusive sting 
in the sucker situated at the posterior extremity. 
4 With Echinococcus, Coenurus, and Cysti- 
cercus, the number of hooks is twenty to thirty ; 
and I have seen as many with Taenia scolecina, 
and infundibuliformis ; but I have found only 
eighteen with Taenia angulata, ten with T'aenia 
setigera, and eight with T'aenia lanceolata. 
Taenia scolecina, crassicollis, and Cysticer- 
cus, have an equal number of large and small 
hooks alternating with each other, and, at a cer- 
tain point, forming a double circle. 
With Taenia, and especially those which have 
these organs on the proboscis, they may be partly 
or even wholly detached. 
Rudolphi has regarded Taenia gracilis, angu- 
lata, infundibuliformis, setigera, and stylosa, as 
naturally without these organs, but I have often 
found them having a complete circle. 
With Taenia cucumerina, the structure is dif- 
ferent ; its seven rows of hooks are in all respects 
like those of Echinorhynchus. 
5 See Lebiond, Ann. d. Sc. Nat. VI. 1836, Pl. 
XVI. fig. 5,6, 7; and Goodsir, Froriep’s neue 
Notiz. 1841, No. 429, fig. 18; also Mayer, Mil- 
ler’s Arch. 1842, Taf. X. 
