residing in the Tubular Organs of Sharks and Rays. 13 



interior of these vesicles or tubes is divided into compart- 

 ments by longitudinal septa or divisions ;" but this is an 

 error which does not require any refutation. The contained 

 gelatinous matter is perfectly cylindrical, and the tubes, 

 though they appeared to me homogeneous in texture, were 

 found to be composed of fibres perpendicular to the axis of the 

 tube. I am indebted for this fact to Dr. Brewster, who at my 

 request examined several of the tubes under a microscope of 

 high powers. Dr. Brewster, at the same time, mentioned to 

 me his suspicion that the fibres, of which the tubes were 

 very evidently composed, were not circular, but spiral, and 

 that the whole tube might thus be composed of a single fibre. 

 The tubular organs undergo various modifications, accord- 

 ing to the tissue in which they are placed, and according to 

 the nature of the parts they have to pass through on their 

 way to the surface ; on the snout, they do not appear to reach 

 the skin entirely, at least every where, as there is interpos- 

 ed a thick cartilaginous lamina into which they scarcely 

 penetrate ; and accordingly, though most abundant on the 

 upper and lower surfaces of the snout in the tope, by no arti- 

 ficial pressure can the gelatinous or vitreous contained mat- 

 ter be forced through the pores of the skin, which neverthe- 

 less are here very abundant. On the other hand, around the 

 mouth, and even the orbits, the gelatinous matter can be 

 forced through the pores of the skin by very gentle pressure. 

 In some parts of the snout, the tubular organs approach 

 quite close to the integuments ; they become much firmer, 

 and of a transparent horny texture ; when cut through, a 

 mass of them greatly resembles a honey comb. Over the or- 

 bits they run in long tubes, having parietes of a dense white 

 fibrous structure, but are still evidently the same organs, and 

 perhaps having their roots in the one or other of the two 

 great gelatinous masses placed on either side' the snout, form- 

 ing the great bases of the tubular organs. The latter are, 

 however, rather imbedded in the large gelatinous mass, and 

 do not absolutely seem to grow from it ; that is, the large 

 branches of the fifth pair of nerves penetrate into these masses, 

 and dividing into extremely numerous and detached branches 

 send one to each of the tubes. The tubes are entirely shut at 

 the extremity next the nerve. I did not observe any thing 

 peculiar in their peripheral extremities. When we remove one 



