CHAPTER IV 

 THE INTEGUMENT AND THE EXOSKELETOX 



" Seit Huxley seine Schrift ' Zeugnisse fur die Stel- 

 lung des Menschen in der Natur ' veroffentlicht hat, 

 sind 31 Jahre vergangen, und wenn man erwagt, was 

 in diesem Zeitraum auf dem Gebiet der physischen 

 Anthropologie, der Embryologie und Morphologic 

 iiberhaupt gearbeitet und erreicht worden ist, so ist es, 

 meine ich, an der Zeit, den Blick wieder einmal ruck- 

 warts zu richten, das zu einem einheitlichen Ganzen 

 zusammenzufassen, was an vielen Orten zerstreut 

 liegt, un daraus endlich zu ersehen, was der Mensch 

 war, was er ist, und was er sein wird." 



ROBERT WIEDERSHEIM, Der Bau des Menschen, 



1893, P- 3- 



THE usual invertebrate form of integument is composed of 

 a single layer of epidermic cells, the external surface of which 

 is covered by a non-cellular structure formed from the cell 

 walls. This outer element is often a transparent cuticula* or 

 in other cases may consist of vibratile cilia. Beneath the in- 

 tegument, and separated from it by a thin layer of connective 

 tissue, lie the muscles. 



The integument of Amphioxus conforms to this general 

 type, but in all true vertebrates important changes take place, 

 rendering it quite different in structure and of far greater 

 complexity. The epidermis becomes many-layered and loses 

 the external cuticula, although cilia persist in a few early 

 larval forms, and the underlying connective tissue becomes 

 thick, often much exceeding the epidermis in this respect. As 

 this latter layer, the corium [cutis~\, is almost indissolubly as- 



* The flattened outer cells of the epidermis, which form the stratum cor- 

 neum, are, under certain circumstances, easily separated from the next, 

 and form a thin layer often termed the "cuticle." The use of the word 

 in this connection is questionable, on account of its liability of being 

 confused with the non-cellular cuticula of invertebrates 



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