1S89.] *^00 [Ryder. 



class of fibres having a direction wbicli is vertical to the outer surface of 

 the body. 



In the other groups the fibrous layer or corium departs more or less 

 from this primitive arrangement; the type which presents the least depart- 

 ure from the arrangement of the elements of the two integumentary lay- 

 ers of fishes are the Batrachia. Above the Batrachia, the subcutaneous 

 layer begins to show the fibres running irregularly without such an ob- 

 vious arrangement of laminte. This is the case in Replilia, but in Aves, 

 over the feathered areas, there is a tendency for the fibres of the corium 

 to be disposed in coarse quadrangular or lozenge-shaped meshes, the decus- 

 sations of which correspond to the points of insertion and mode of ar- 

 rangement of the deeply implanted feathers. 



In Mammalia there is the greatest variation in the thickness of the epi- 

 dermis. In the elephant the epidermis is quite thin, but the corium in 

 the most exposed parts is of enormous thickness and contains a great propor- 

 tion of elastic fibres, that kind of tissue reaching a most phenomenal de- 

 velopment in this form, even invading the adipose and muscular tissue in 

 all parts of the body of the animal. 



In the Cetacea and hippopotamus the epidermis is much thickened and 

 the papillse of the corium greatly elongated. These two forms are amongst 

 those which depart most widely from the usual type characteristic of 

 Mammalia, in that in the first the sudoriferous glands appear to be wanting, 

 and the corium is rudimentary, while in the latter they are modified into 

 the remarkable organs concerned in the secretion of the red exudation, 

 "bloody sweat, " which has been noticed by many writers, but which 

 was never adequately studied until examined b}' Max Weber* 



The development of the glands of the skin, which are always in direct 

 genetic relation with the epidermis, opens up questions of considerable 

 phylogenetic interest, and to call attention to these is the purpose of the 

 present note. If we tabulate the classes of vertebrates according to the 

 degree of development of the dermal glandular organs some singular as 

 well as interesting contrasts are brought out and clear evidence of the 

 method of evolution of these organs is also obtained. 



A. — 1. The fishes (selachians, teleosts, etc.) tend to develop numer- 

 ous scattered unicellular glands of the skin, as goblet cells. 



These single-celled structures have doubtless multiplied side by side 

 and given rise, first, to a pit, then by further invagination to a flask-shaped 

 glandular appendage of the epidermis, somewhat according to the method 

 suggested by Lang, f In this way the simplest form of epidermal gland, 

 such as is seen in the Batrachia, may be supposed to have arisen. 



It is at least suggestive that the persistence of goblet cells in the ali- 

 mentary tract and bladder of some forms (the bladder being primarily a 

 diverticulum of -the intestine) is an inheritance from the gastrulated stage 



* Studien liber Siiugethiere. Eiii Beitrag zur Frage iiacli dem Ursprimg dcr Cetacean. 

 8vo, Jena, 18S6. 

 t Lehrbiicli der Vergleichenden Anatomic, Svo, Jena, 18S8, p. 39, Figs. A, C, D, E. 



