1894.] NEW-YORK MICROSCOPICAL SOCIETY. 43 



it all, as there is no general work on the subject that I have yet 

 found — no manual which treats of the anatomy and physiology of 

 the skin in a comparative sense, with a section devoted to micro- 

 scopical methods. The need for such a work is evident. 



Owing to this magnitude I can only speak of generalities. I 

 will first say a few words of the skin in general ; then take up the 

 several types of vertebrates, and speak of their most characteristic 

 structures as derived from the skin ; and finally make brief men- 

 tion of the theories of homologies and correlations that have been 

 noted in the higher types. 



II. The Skin in General. 



The vertebrate skin, as derived from the embryo, consists of 

 two layers, a superficial ectodermal and a deeper mesodermal 

 layer. The former is called the epidermis (scarf-skin), the latter 

 the dermis (corium or cutis). The skin, like a mucous mem- 

 brane, consists of an epithelium resting on a connective-tissue 

 basis, the epithelium forming the epidermis made up of a few 

 or many layers of cells. The surface of the dermis is thrown 

 up into a number of elevations, called papillae, which differ 

 in form, size, and complexity in different regions of the body 

 and with the position in the animal scale. I'he epidermal or 

 outer layer does not follow this papillary contour of the dermis, 

 and when the two layers are carefully pulled apart and examined 

 ie-g., in the human skin) the papillae appear to plunge into and 

 be covered by the more even epidermis, although the outer sur- 

 face is well marked by ridges and furrows, such as we can plainly 

 see in the palm of the hand. These papillae are the end organs 

 of that most important sense, touch, and in the lower forms may 

 also function as other sense organs, which will be spoken of 

 later on. 



The outer or epidermic layers always consist of cells only, 

 while the derma is made up also of connective-tissue fibres, as 

 well as of elastic and contractile elements. In the epidermis two 

 layers can' always be distinguished — an outer, composed of horny 

 cells, and therefore called the stratum corneum j and an inner, 

 made up of soft protoplasmic cells, the stratum Malpighii. The 

 latter really serves as a matrix for the regeneration of the outer, 

 horny layer, the superficial part of which is continually scaling 



