CHITIN IN THE CAETILAGES OF LIMULUS AND SEPIA. 181 
hydrochloric acid in the cold, from which solution it was 
reprecipitated by the addition of water in the form of white, 
colourless flocculi. 
It was also soluble in concentrated sulphuric acid ; this was 
diluted and boiled, and then was found to possess the property 
of reducing cupric salts. 
These preliminary tests clearly pointed to the body being 
chitin ; its solubilities and insolubilities are of themselves 
almost characteristic of this substance. 
The indication was rendered a certainty by boiling the 
colourless solution in hydrochloric acid ; in about half an hour 
it became dark brown, owing to the formation in it of the 
hydrochlorate of glycosamine as in the previous cases. 
Till now the generally received opinion has been that chitin 
occurs solely in epiblastic structures; Ewald and Kuhne 1 found a 
body resembling it in the nervous system of Crustacea, but 
this also is epiblastic. In the nervous system of these animals, 
it seems to replace what Kuhne calls neuro-keratin, a horny 
substance occurring in the nerve-fibres of vertebrate animals. 
But it is clearly not confined to the epiblast ; for in three 
instances chitin has been now shown to occur in mesoblastic 
structures, viz. in the cartilage of the cuttlefish and king-crab, 
and in the liver ' 2 of the latter animal. 
1 Ewald u. Kuhne, “ Ueber einem neuen Bestandtheile d. Nervensystem ” 
‘ Heidelberg Verhandlungen,’ 1877. 
2 If the chitin, present in the liver, is in the liver-cells, not in the connec- 
tive tissue as above supposed, we have an instance of chitin occurring in 
hypoblast. 
