ox THE CORPUSCULA TACTUS 289 



tion of the stalk of the vesicle. A nervous bundle passes through the 

 stalk, accompanied by a vessel, and branches out in the knob ; its 

 fibres become pale and terminate here, not passing through as Savi 

 stated. (Diag. C.) 



In the Rays and Sharks, bodies precisely similar to these, open by 

 a tubular neck upon the outer surface of the skin. In the Sharks 

 they have no special external hard capsule, while in the Rays they are 

 provided with such a capsule, composed of condensed connective 

 tissue. (Diag. D. E.) 



In the osseous Fishes, ampullae, similar to these, connected together 

 by a longitudinal tube open on the sides of the body along the so- 

 called lateral line. The s}-stems of each side are connected by a 

 transverse tube which passes over the occiput. In the Sharks and 

 Rays, organs of an exactly similar nature form a system of ramifying 

 tubes in the head and over the sides of the body. These organs have 

 hitherto been known as the " muciparous canals ; " though, as Leydig 

 has well shown, they contain a semi-solid gelatinous material, and 

 have nothing to do with the mucus of the skin, which is formed by 

 the altered epidermic layer. As Leydig has pointed out, then — the 

 Pacinian bodies, the Savian bodies, and the so-called nmciparoiis canals 

 of osseous and cartilaginous fishes are homologous organs, and form 

 a series, whose lowest term, if Wagner's conclusion be correct, is 

 formed by the corpiiscida tactus. What is the highest term ? In the 

 most complex ampulla, or muciparous canal, of a Ray or Shark, we 

 find — I. externally a thick coat, composed of condensed connective 

 tissue ; 2. a nervous twig penetrating this, and passing to — 3. an 

 internal delicate sac, which contains a gelatinous matter, communi- 

 cates with the exterior, and is lined by a layer of cells continuous 

 with the epidermis : on the walls of this the vessels and nerves termi- 

 nate. Now, we have only to conceive a single hair, developed within 

 one of these ampullse and taking the place of the clear gelatinous 

 matter, to have a vibrissa, such as is met with in almost all the Mam- 

 malia about the lip and eyebrow (see Diagr. F) ; and I conceive that 

 the vibrisscB are, in fact, the most complex and fully developed forms 

 of this series of cutaneous organs. ^ Now, the vibrissa: are, without 

 doubt, delicate organs of touch, and the mucous canals of Fishes 

 appear to be very probably of the same nature ; but when we come 

 to the Savian and Pacinian bodies, and to the Corpuscula tactus, two 



' The auditory labyrinth is constructed on precisely the same plan as the muciparous 

 canals of fishes, and the eye on that of a vibrissa, as might readily be demonstrated ; so that 

 all the organs of sense are to be regarded as modifications of one and the same plan. 



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