HISTOLOGICAL EQUIVALENTS AND SUBSTITUTIONS. 99 



kind of epithelium from every kind of connective tissue, 

 but only where scaly epithelium is met with, whilst the 

 limits are doubtful wherever cylindrical epithelium exists. 



Just in the same manner elsewhere also do the bound- 

 ary lines become obliterated. Whilst formerly the lim- 

 its which separate the elements of muscle from those of 

 tendon were considered to be most distinctly defined, 

 extremely decisive proofs have in this case also been 

 afforded, and first by Hyde Salter and Huxley, that fibres 

 proceed from connective-tissue corpuscles, which whilst 

 pursuing their course in an inward direction, all at once 

 assume the character of transversely striped muscle. So, 

 then, in the case of connective tissue, it would seem 

 there exists a continuous connection between the ele- 

 ments of the surface and the more highly developed ones 

 of the deeper parts. Now if, on the other hand, it has 

 turned out to be very probable that the corpuscles of 

 connective tissue have definite relations to the vascular 

 system, we are, as you see, almost justified in regarding 

 this tissue as a kind of neutral ground for parts to meet 

 upon (indifferenter Samelpunkt), as a peculiar arrange- 

 ment for their intimate connection, an arrangement 

 which, though certainly not exercising any great influence 

 upon the higher functions of the animal, is yet of great 

 importance as far as its nutrition is concerned. 



In the place of the law of continuity, therefore, we 

 must necessarily put something else. And here, I think, 

 the doctrine which has the strongset claims to our atten- 

 tion is that of histological substitution. In the case of 

 all tissues of a like nature it is quite possible, even 

 whilst confining our attention to what occurs physiologi- 

 cally in the various classes of animals, to find one tissue 

 at a certain fixed point of the body replaced by an analo- 

 gous one belonging to the same group, or, in other \ 

 words, by an histological equivalent. 



A spot invested with cylindrical, may acquire scaly. 



