^10^ 



THE IIELMIXTIIES. 



107 



The young of Echinococcus, Coejiurus, 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. Each 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. The length of the sheath, which is usually enlarged at its base, 

 depends upon that of the proboscis. 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. Usually their size decreases from before backwards, so that those 



the suctorial apparatus of the Trematodes. In Tris- 

 tomum hamatum (see Rathki, 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. 

 Beiträge, Hft. I. p. 82, Taf. V. fig. 6, 7), the borders 

 of the si.x 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 tlie 

 posterior extremity of Octobothrium sagittatum, 

 Merlangi, and of Diplozoon paradoxum ; an 

 analogous support wholly surrounds the large foot 

 at the end of the body of Axine {Leuckart, Zool. 

 Bruchstücke Hft. 3, Taf. II. and Nordmann, 

 Micogr. Beitr. Hft. 1, Taf. VII.; also Diesins:, 

 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 

 (JJiesing, Ann. d. Wiener Mus. I. Abth. 1, Taf. 

 III. IV.). A remarkable exception among the 

 Nematodes is found with Hedruris androphora, 



of which Nitzsch (Ersch and Gruber^s Encyclo- 

 p£ed. VI. p. 49, IX. 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 infundibu liformis ; but I have found only 

 eighteen with Taenia angulata, ten with Taenia 

 Setigera, and eight with Taenia 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 espe(;ially those which have 

 these organs on the proboscis, they may bfe partly 

 or even wholly detached. 



Rudotphi has regarded Taenia gracilis, angu- 

 lata, infundibuliformis, setigera, and stylosa, as 

 naturally without these organs, bvit 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 Leblond, Ann. d. Sc. Nat. VI. 1836, PL 

 XVI. fig. 5, 6, 7 ; and Goodsir, Froriep''s neue 

 Notiz. 1841, No. 429, fig. IS } also Mayer, Mut- 

 ter's Arch. 1842, Taf. X. 



iGoi^ ^•^ V\^\ 

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