OF THE INVERTEBRATE ANIMALS. 25 



cient quantity. The cutaneous system, however, of all those 

 species which were examined {Phalangium parietinum, Alius 

 scenicus, Epeira diadema and Tegenaria domestica) gave the re- 

 actions of chitine. In Epeira, the fibrous layers are very distinctly 

 seen even before they have been ti'eated with potash : the sepa- 

 rate fibres here form elegant undulating lines, which are coiled 

 around cylindrical depressions in the upper layer (these are for 

 the reception of the long hairs). The entire aspect, as also the 

 hairs, remain unaltered after treatment with potash, the pigment 

 disseminated between them being dissolved. 



We have, then, in the remarkable agreement of form and 

 composition, another common hnk in the characteristics of the 

 Articulata. A comparative histo-genesis would also be of great 

 interest; but with reference to this, very little has been done: 

 older works, which are still classical in another point of view, 

 give us no assistance here*. 



Now in what relation does this chitine, a substance which, as 

 we have seen, is widely diffused through the animal kingdom, 

 stand to the other important constituents of the animal or vege- 

 table organism, to albuminates, the so called hydrates of carbon, 

 &c.? The solution of this question is of great interest. We 

 find it, as we have seen, only in the Articulata, those three families 

 of the animal kingdom, which, being inclosed in a more or less 

 solid tegument, are compelled to overcome this obstruction to 

 their internal growth by periodically casting off their armour. 

 In many, and these are the largest (Crustacea), the annual for- 

 mation of the tegument is well known : an enormous quantity of 

 formative material must be generated in a short time for the re- 

 production of these cast-off envelopes. This material, as we have 

 seen, is chitine, a substance which cannol be generally proved to 

 exist under a similar arrangement of its elements in the animal 

 or vegetable cell, and yet these chitinophores form their mantle 

 from both animal and vegetable food. 



If, for comparison, we admit man to form " the standard 

 and measure of creation,^' we here apparently find for a short 

 period an enormous distinct production of matter — I allude to 

 that of the milk during the earlier periods after child-birth. But, 

 as I have stated, this is only apparent ; it is in reality a mere 

 alteration in position and form which strikes us, which the former 



• As Rathke's History of the Development of the Craw-fish, Treviranus's 

 treatise on Spiders, &n. 



