^§ 105, 106. 



THE HELMIXTHES. 



Ill 



CHAPTER IV, 



ORGANS OF SENSE. 



§ 105. 



The sense of touch is probably the only one well developed with the Hel- 

 minthes. The granulations, warts, papillae, filaments, and retractile lobes, 

 found upon the head of some species,*" are, without doubt, the organs of 

 this i'unction. Tiie red and black points upon the back of many, both adults 

 and larvae, and which have been regarded by some naturalists as organs of 

 vision, appear to be only pigmentary spots ; for they contain nothing like a 

 light-refracting body.'-' 



CHAPTER V. 



DIGESTIVE APPARATUS. 



§ 106. 



degree 



of 



The di2;estive organs with the Ilelminthes have a variable 

 development in the different orders. 



In the Cystici, Cestodes, and Acanthocephali, neither mouth nor alimentary 

 canal is perceived. In the first two order?, there is, however, a system of 

 vessels which may be regarded as a digestive apparatus; but these are 

 designed for circulation, rather than for digestion, since their walls are com- 

 plete throughout and have no openings, as has erroneously been supposed, 

 which communicate with the suckers of the head ; and their contained nutri- 

 tive material is received by them through the skin in an endosmotic manner.**' 



• These tactile granulations are found with many- 

 species of Ascaris, as, for instance, in Ascaris 

 osculata, between the large oral collars ; iu Physa- 

 loptera alata, they surround the oral extremity of 

 the body as a single row ; but they form a double 

 one in Ascaris trunculata. With Distomum 

 iaureatum, and nodulosum, they are found upon 

 the borders of the oral sucker. With Holostomum 

 excavatmn. und podomorphum, there are two re- 

 tractile lobules protruding from the sides of the 

 mouth ; and in Holostomvm alatum, these have 

 antenna-like filaments ; see Ifiizsch's figures of 

 Holostomum, in Erse h and Gruier's Encvclop. 

 III. p. 399. IX. 



■2 These dark pigment-dots upon the infusori- 

 form embryos of many Trematodes when they es- 

 cape from the eg?, and of which there is only one 

 upon the neck of Distomum nodulosum, and. hians, 

 and two upon Monostomum mutabile, have been 

 taken for eyes by Nordmann (Microgi-. Beitr. Hft. 

 2, p. 139), and formerly by myself also \wiet;- 

 tnann's Arch. 1835, I. p. 69, Taf. I. fig. 3, 4, 5). 

 Three of these dots have been observed upon a 

 larva of a Monostomum which Nitzsch (Beitr. 



7,ur. Infusorienkunde, p. 29, Taf. I.) has described 

 in Cercaria ephemera ; I have seen only two 

 upon the back of many cercarian larvEe. Of this 

 same nature are the two red dots of Scolex poly- 

 morphus (Muller, Zool. Danica. Tab. LVIII. fig. 

 16, IT), as also the brown ones upon the neck of 

 Gyrodactylus auriculatus {Nordmann Jlicrogr. 

 Beitr. Hft, I. p. lOS, Taf. X. fig. 4). Finally may 

 be mentioned Amphistomum subclavatum. which 

 has two large oval black dots upon its neck. These 

 pigment-c -'Us are physiologically, without doubt, 

 simply colored spots, which in Folystomum inte- 

 gerrimum are highly developed, forming a widely- 

 spread suljcutaneous net-work. Sometimes, and 

 especially in the various Cercariae, and in many in- 

 dividuals of Amphistomum. subclavatum, these 

 dots have a very effaced aspect ; this is probably 

 due to a dissolution of the walls of the cells, — the 

 pigment-granules being then scattered through the 

 skin. 



1 It has already been observed that the four 

 suckers of Taenia, regarded by Nitzsch as oral 

 orifices, are imperforate at their bottom. Ouen 

 (Cyclop. Anat. &c. II. p. 131) has fallen int/^ r. 



