APPENDIX. 459 



These four substances all yield leucin and glycocine on decom- 

 position. 



Hyalin is allied to chitin, and is found in the Echinodermata 

 and other Invertebrates. It has the following composition : — 

 C- 45-3*044.1; 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 Ticnicata, Oiyhnj- 

 dium, kc. It is represented by the formula (CpH,QO.)„.* 



IV. The Ink-bag of 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 ei seq.) denotes wave-lengths. For instance, 

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

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



* For further information, see Gautier's Chimie Biologique (iSgz), pp. 163, 

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

 t Chem. CentrulbluU, 18SS, p. 5S7. 



