108 THE HELxMINTHES. '^ 104. 



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 neclc. 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 protens, 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 muscuhir 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 Ilelminthologists are not yet agreed as to the a sting which projects from the back above the 

 number and arrangement of ttie proboscideal mus- oral sucker (and not from the mouth itself, as fVair- 

 cles of thi; AcanthocephaU ; see Nitzsch, in Erscli ner has supposed, Isis. 18:34, p. 131), and which 

 and Onihfr^s Eiicyclop. I. 1818, p. 2^2 ; Bojanus, serves to open a passage through the parenchyma 

 ill Isis, 1821, Taf. III. fig. 34 ; IVestrumb, De of the animals they infest. An entire group of 

 lltUnintliibus Acanthocephalis 1821, p. 50 ; and Distomum, as Distnmum echinatian, milltare, 

 Cloquet, Anat. des Vers, intestin. p. 76, PI. VII. uncinatum {Bremser, Icon. Helminth, Tab. X. 

 Me.lUis (Isis 18;31,-p. 82) has taken the probosci- fig. 5), which Rudolphi has designated as Echinos- 

 deal sheath for an uesophageal organ, and its two tomata, have around their oral sucker an annular 

 muscles for vessels. Burow (Echinorhynchi stru- collar, upon which are numerous straight spines 

 mosi Anatome, 1836, p. 16, fig. 1, e) has fallen arranged in a circular "manner. An armature of 

 Into a similar error, in regarding these same mus- this kind is found upon a Cercaria. These spines 

 cles as intestinal tul)es. are as easily detached as the hooks of the armed 



7 With many Trematodes, as, for example, with Taeniae. With Spiroptera crassicauda, I have 

 PolyKtomum, Or,tobnthrium,tfC. (see Baer, Nov. found on each side of the mouth a doubly-pointed 

 Act. Acad. Leop, Carol. XIII. pt. 2, Tab. XXXII. sting pointing backwards, and behind this two 

 fig. 7, f. and Mayer, Beitrage, &c., Taf. III. fig. others three-pointed. A still more remarkable 

 3, m. m. fig. 8), there are found between the suck- form is seen in the four jjenniform stings, which 

 ers at the posterior extremity, speciid hooks, and project behind the mouth of Jiiri/nii:iiiithu.i 

 to which, with Po/ystomitm, I have seen proper pinnali/idii.i (see 7J('esm§-, Ann. d. Wiiner Mus. 

 muscles proceed from the interior of the body. II. Abth. 2, Taf. XIV. XVIII.). These Nematodes 



With certain Ccrcar we(larva! of Distomum) one undoubtedly use these instruments for piercing tlie 

 lan distinctly observe the use which they make of stomachal membranes of the animals they infest. 



