504 



TEGUMENTARY ORGANS. 



perfect connective tissue occupying the centre 



of the papillae, and further distinguished by 



having their endoplasts and imperfect elastic 



Fig. 320. 



A papilla with its Corpusculum tactus surrounded by 

 three vascular papillae. 



fibrils arranged transversely to the axis of the 

 papilla, so that they appear to be made up of 

 transverse superimposed laminae (fig. 320.). 

 One or two dark- contoured nerve tubules come 

 up through the base of the papilla, and running 

 along one side of the corpuscles, thin out and 

 terminate, without, so far as I have been 

 able to see, entering its substance. In fact, 

 these nerve tubules are, as Kolliker pointed 

 out, accompanied by a delicate neurilemma, 

 and the axile corpuscle itself appears to me 

 to be nothing more than the enlarged end 

 of this neurilemma. 



In Birds, a large proportion of the tegumen- 

 tary nerves terminate in bodies which are, on 

 the one hand, related to these axile corpuscles, 

 and on the other to the well-known Pacinian 

 bodies (fig. 322). They are, in fact, usually 

 described under the latter name; but their small 

 size and superficial position, the paucity of their 

 concentric lamellae, and the transverse striation 

 of the solid central axis, ally them closely with 

 the corpuscula tactus. They are found in the 

 skin around the sacs of the feathers, in the 

 beak, and in the interosseus spaces of the fore- 

 arm and leg. 



A special article (PACINIAN BODIES) has 

 already been devoted to the organs of this 

 kind which are met with in Mammalia, and 

 it need only be added here, that late re- 

 searches have shown that the Pacinian bo- 

 dies of mammals, like those of birds, are 

 solid masses of rudimentary connective tissue; 

 the appearance of capsules and of a central 

 cavity, arising merely from the arrangement of 

 the elastic element and the extreme transpa- 

 rency of the collagenous substance. * They are 

 in fact nothing but thickened portions of the 

 neurilemma, and the nerve which they enclose 

 either passes through them, or more usually 



* This fact was ascertained and stated indepen- 



terminates, more or less abruptly, in the cen- 

 tral solid axis. 



In the article on the PACINIAN BODIES re- 

 ference is made to the peculiar organs de- 

 cribed by Savi in the Torpedines. These 

 Savian bodies, in fact, are little more than 

 Pacinian bodies converted into sacs by the 

 development of a cavity between their cen- 

 tral and peripheral portions. Now Leydi" 

 has discovered that these feavian bodies do 

 not stand alone, but that they form a part of 

 a great series of peculiar integumentary sen- 

 sory organs, which are most characteristically, 

 if not solely, developed in the class of Fishes 

 the so-called mucous canals and follicles. 

 It has long been noticed, in fact, that in 

 osseous fishes one series of the scales along 

 the sides of the body differ in their structure 

 from the rest, giving rise to what is called the 

 lateral line; and that a canal runs beneath 

 these scales from the tail to the head on each 

 side ; that then becoming connected with its 

 fellow by a transverse branch over the oc- 

 ciput, each canal passes forward on the 

 sides of the head, dividing into two principal 

 branches, one of which following the course of 

 the suborbital bones terminates at the end of 

 the snout, while the other passes down on to 

 the lower jaw. Similar organs, but having a 

 more complicated arrangement, are known to 

 exist in the cartilaginous fishes ; but it is com- 

 monly supposed that these canals and follicles 

 secrete the mucus with which the skins of 

 fishes are lubricated. However, in a very beau- 

 tiful series of researches, Leydig has shown 

 that the mucus is furnished by the cellular 

 ecderon, and that the so-called mucous canals 

 and follicles are sensory organs. The limits 

 of this article will not permit me to enter 

 into any of the details of structure of these 

 organs, but they may all be described generally 

 as sacs or canals lined by a cellular investment 

 like that of the skin upon which they open,' 

 and filled with a more or less gelatinous sub- 

 stance. If the organ be a sac, a single pro- 

 tuberant knob, if a canal, a series of them pro- 

 ject into the cavity. Each knob is covered 

 by a coat consisting of tiers of much-elongated 

 cylindrical cells. Its substance consists of 

 niore or less gelatinous connective tissue, and 

 it receives a nerve (a branch of the fifth or of 

 the vagus), whose fibres divide and become lost 

 in its tissue. In the osseous fishes this nerve 

 usually perforates the peculiarly modified scale 

 of the lateral line, which supports and encloses 

 the canal at these points. In the cartilaginous 

 nsnes, the canals have sometimes special fibro- 

 cartilaginous coats; or if sacculi, a number of 

 them may be contained in a common cartila- 

 ginous investment, as in the Chima?ra. Leydi" 

 insists with great justice on the identitv of 

 the structure of these organs with that of the 

 semicircular canals of the ear. 



The connection of these sacs and canals with 

 the corpuscula tactus and Pacinian bodies 



dently and contemporaneously in 1853, by Leydur 

 and myself. See Quarterly Journal of Mk? 

 Science No. V., and Siebold and Kolliker's Zeit- 

 schnft, B. v. Heft 1. 



