22 SCHMIDT ON THE COMPARATIVE PHYSIOLOGY 



tissue, are of physiological importance j it will not therefore be 

 superfluous to state them. 



1-710 of the thoracic shield of the Craw-fish (dried at 248° F.), 

 when heated to redness, yielded, after the deduction of the 

 carbon left undissolved on exhaustion with dilute acid, 0-91 1 

 fixed substances, 0-120 of which consisted of phosphate of lime 

 with a little magnesia (precipitated by ammonia); 0-4615 of 

 Squilla mantis gave 0-l7l5 fixed residue, containing 0-090 phos- 

 phate of lime. 



3-023 of the claws of the Lobster gave 2-3295 fixed residue, 

 containing 0-281 phosphate of hme ; thus we have — 



Craw-fish. Squilla. Lobster. 



Chitine 46-73 62-84 22-94 



Lime-salts . . . 53-27 37-17 77*06 



100 parts of ash consisted of — 

 Craw-fish. 

 Phosphateof lime . 13-17 

 Carbonateof lime . 86-83 



We find here the interesting result, that the amount of earthy 

 phosphates increases in proportion to the quantity of organized 

 chitine-tissue ; this is confirmed by former analyses of the shell 

 of the lobster, craw-fish and Cancer pagurus made by Merat- 

 Guillot*, Chevreult and GobelJ. 



This fibrous chitine-tissue is however the result of an active 

 process of cell-formation during the change of the shell ; the 

 quantity of phosphate of lime also increases with the intensity of 

 this process, for which the relative amounts of tissue formed 

 yield the standard. Hence the phosphate of lime must be in 

 intimate relation with the process of cell-formation. 



It is evident from the following observations, that the chitine- 

 tissue really owes its origin to such a process. 



By carefully removing a portion of the thoracic or mandibular 

 shell in layers down to the uppermost pigment layer of the mem- 

 brane lying beneath it, I induced a new process of cell-formation. 

 This soon took place ; in eight hours, a thick, tenacious, trans- 

 parent mass [cytoblastema) had already exuded ; in it I found 



* Annales de Chimie, xxxiv. p. 71. 



t //w«. Gen. des Sciences Plujs. iv. p. 124 ; also Schweigger's Journal, xxxil. 

 p. 49.5. 



+ Schweigger's .Tourn. xxxix. p. 411. They are all collected in Heusinger's 

 IJintvloyie, ii. p. 2.53. 



