APPENDIX. 459 



These four substances all yield leucin and glycocine on decom- 

 position. 



Hyalin is allied to cHtin, and is found in the Eohinod&rmata 

 and other Invertebrates. It has the following composition : — 

 C = 45-3 to 44-1 ; H = 6.5 to 6.7; N= 5.2 to 4.5; = 43 to 44.7 per 

 cent. 



Tunicin is the carbohydrate found in the Tunicata, Ophry- 

 diuni, &c. It is represented by the formula (CuHijO^),,.* 



IV. The Ink-bag op Sepia. 



The secretion of the ink-bag (see p. 73) is used to colour the 

 water and cover the flight of the animal. It contains from 70 to 

 87 per cent, of solids, of which the black or brown pigment is the 

 chief constituent ; it also contains mucin, magnesium carbonate, 

 sodium sulphate, calcium carbonate, and sodium chloride. Accord- 

 ing to Nencki and Sieber,f the pigment contains an acid, which 

 has been termed sepiaic acid. 



It has been suggested that the ink-bag corresponds to a liver ; 

 but its secretion contains neither biliary acids nor glycogen, and 

 it has no digestive properties. 



V. Wave-lengths. 



The sign X (p. 151 et seq.) denotes wave-lengths. Por instance, 

 X506 means a wave-length equal to 506 milhontfis of a millimetre. 

 Sometimes the letters W.L. are used instead of X. 



* For further information, see Gautier's Chimie Bwlogique (1892), pp. 163, 

 165, 188 ; and Halliburton's Chemical Physiology and Pathology. 

 t (Jherri: CentralUaU, 1888, p. 587. 



