Dr. J. Murie on the 8km &c. of the Rhytina. 311 



Unfortiinatelj Dr. A. Brandt's figures of the skin's struc- 

 ture in its natural dimensions are too large for me to repro- 

 duce here; I can only afford room, therefore, for a little bit, 

 and that where the elevations and furrows are smallest, vide 

 fig. 3. He shows in other views enlargement of the papillary 

 and scaly prominences, and widening and greater continuity 

 of the furrows. 



Short finer hairs and coarser bristles are sparsely dispersed 

 among the crevices ; but, as I gather from the text, they, re- 

 latively to the size of the animal, are neither so long nor so 

 abundant as in the Manatee. 



The inner surface of the piece of skin in the St. -Petersburg 

 Museum, whilst almost smooth compared with its exterior 

 surface, yet shows slight inequality by circular, fiat, dome- 

 shaped areas. These are more regular in size and shape, but 

 withal appear to coiTespond somewhat to the external papil- 

 lary elevations. 



Steller's original description of the intimate composition of 

 the skin, namely its marked tubular character, led in part to 

 the idea of its being a cuticular substance sui generis. It was 

 suggested that its peculiar composition, an outer scabrous 

 coat and cylindrical layer beneath, might be an adaptation 

 designed to protect the animal from ice-floes &c. and retain 

 internal heat in an inhospitable climate, so different from the 

 tropical regions inhabited by Manatus. 



Prof. J. F. Brandt, however, previously to the finding of the 

 piece of skin in question, wisely, I think, correlates the dermal 

 covering of Rhytina to that of the Manatee. 



Dr. Alex. Brandt's recent thorough microscopical examina- 

 tion of the Rhytina's skin renders clear all difficulties as to its 

 constituents. He demonstrates by well-drawn figures the 

 nature of the so-called tubules &c. A vertical section, viz. a 

 small piece dragged off by the nail from the specimen softened 

 in water (fig. 4 in our Plate), shows three layers, whereof the 

 middle, thickest and darkest one is composed of upright, closely 

 set, linear columns, the supposed tubules. Under a higher 

 magnify ing-power the cuticular papillae are found to be com- 

 posed of a series of epithelial cells. These, from being more 

 densely packed in some parts than in others, give the cylindrical 

 character to the derm, which is more or less of horny consistence. 

 In other figures of horizontal slices from the surface downwards, 

 irregular-shaped vacuola with pigmental margins are displayed ; 

 these Brandt compares to the Haversian system of fish-bone, 

 to which, indeed, they have much likeness. Deeper they 

 narrow, are rounder and more apart. Their composition is 

 also epithelial, close- or wide-meshed. No trace of glands was 

 met with. 



