220 DR. MICHAEL FOSTER, 



Alle die Zellenschichten, welche den Binueiiraumen des 

 mittleren Keimblattes zugekehvt sind,zeigen nun aber unter 

 sich so viel Gemeinsaraes und sie difFeriren von der ersten Zeit 

 ihves Auftretens audi so erheblich von den Zellenschichten, 

 die aus den beiden Granzblattern hervorgegangcn sind, dass 

 man, im Interesse physiologischen Verstandnisses wohl 

 than -wild, sie von diesen durch eine besondere Bezeicliunng 

 zu scheiden, sei es, dass man sie als undclite Epithelien den 

 dclitcn gegeniiber stellt, sei es dass man sie Endothelien 

 neunt urn mit dem Wort ihre Beziehung zu den innern 

 Korperflachen auszudriicken. 



Endothelium is here contrasted with epithelium, so that 

 the latter may be considered as the "thelium" of free surfaces 

 (whether invaginated or not) , and the former as the " theliura'' 

 of internal closed spaces ; " thelium " apparently being taken 

 to mean " a layer or layers of cells." 



Now, what is the derivation of " epithelium ? " I am in- 

 debted to Dr. Sharpey for the following account. He says, 

 in a letter to me : — " EjntJielium, or rather ' epithelida,^ and 

 especially ' epithelia ' (first declension), was introduced by 

 F. Ruysch. In describing a preparation of the face of a child 

 finely injected, he refers to the cuticle over the red part of 

 the lip (prolabium), and says, ' I cannot call this " epi- 

 dermis," seeing that the subjacent tissue is not skin, but a 

 different substratum covered with sensitive (nervous) papillae, 

 which are finely injected red.' He then goes on to say that 

 as the cuticle lies on papilla3 he will call it epithelida, or 

 epitheliay from £7rt and Qnkr], ' papilla ' or ' mammilla,' and 

 he adds that for the same reason he calls the inside coating 

 of the cheeks by the same name. The original is as 

 follows (Ruysch, F., 'Thesaurus Anatomicus HI/ No. xxiii, 

 p. 16):- 



" ' * * * Nulla sabest huic integumento cutis, ergo epidermis 

 dici nequit quamvis analogiam summam et connexionem cum 

 ilia habet * * * * comperi prolabia constituta esse ex meris 

 papillis non cutaneis (cutis enim hie reveradeest) sedpapillis 

 nervosis ; itaque integumentum illud supradictum potius 

 epithelida dixero vel integumentum papillare prolabiorum 

 quod revera nil est nisi efflorescentia seu expansio extremita- 

 luni papillarum.' 



"In ' Thesaurus Anatomicus VI,' No. cxv, p. 49, he 

 says, ' Anterior pars prolabii inferioris — epithelia adhuc est 

 obducta.' " 



From this it is evident that epithelia, changed in course of 

 time into epithelium, just as platina has become platinum, 

 means " that which covers or is upon a papilla," and conse- 



