66 LECTURE II. 



accumulation of epidermis. It has its origin, as is well 

 known, in a saccular involution of the external skin. At 

 first its connection with the external parts continues to 

 be maintained by means of a delicate membrane, the 

 membrana capsulo-pupillaris ; afterwards this atrophies 

 and leaves the lens isolated in the interior of the eye. 

 The fibres of the lens are therefore, as 0. Yogt has 

 shown, nothing more than epidermoidal cells which have 

 been developed in a peculiar manner, and their regene- 

 ration, after the extraction of a cataract for example, is 

 only possible as long as there still remains epithelium in 

 the capsule to undertake the new formation, and to 

 represent, as it were, a thin layer of rete Malpighii. 

 This reproduces the lens in the same way that the ordi- 

 nary rete Malpighii of the external surface does the 

 cuticle. Amongst the other changes of epithelial struc- 

 tures we shall in due time revert to the peculiar pig- 

 ment cells that are produced in the most different parts 

 by the direct transformation of epidermic cells, the con- 

 tents of which either become coloured by imbibition, or 

 have pigment engendered in them by a (metabolic) 

 transposition of their elements. 



With the history of epithelial elements properly so 

 called is immediately connected that of a peculiar class 

 of structures which play a very important part in the 

 accomplishment of the functions of an animal, namely 

 the glands. The really active elements of these organs 

 are essentially of an epithelial nature. One of "Remak's 

 greatest merits consists in his having shown that in the 

 normal development of the embryo the outer and inner 

 of the well-known three layers of the germinal mem- 

 brane chiefly produce epithelial structures, from a gra- 

 dual proliferation of the elements of which glandular 

 structures arise. Other observers, for example, Kolliker, 

 had indeed before him made similar observations, but by 



