134 PROFESSOR E. RAY LANKESTBR. 



The presence of chitin in a tissue belonging to the skeleto- 

 trophic group, and derived from mesoblast, is a novelty. It 

 appears to have been too readily assumed that the connective 

 tissues of Invertebrata correspond in their chemical nature 

 with those of Vertebrata, and the notion that chitin is a pro- 

 duct confined to the activity of the tissues of the epiblast has 

 been hitherto adopted without a sufficient basis in fact. The 

 skeletal product of the protoplasmic cells which build up the 

 entosteruite of Limulus is chiefly chitin, and I am led, 

 from the behaviour of the fibres and trabeculse of the 

 connective tissue in other regions of the body of Limulus, and 

 in other Arthropoda, to suspect that this substance takes the 

 place of coUogen and chondrin in the skeletal tissues of Arthro- 

 poda. The differences between elastin (the formed substance 

 of Vertebrate elastic tissue) and chitin are so slight that one 

 would not be greatly surprised at the presence of the latter 

 body as a main constituent of connective tissue in some groups 

 of animals were it not for the fact that an attempt has been 

 made by so eminent a physiologist as Kiihne to definitely dis- 

 tinguish between the chemical possibilities of epiblast and 

 raesoblast in regard to this very substance. 



The presence of chitin in the entosteruite of Limulus once 

 and for all establishes the fact that this body can be produced 

 as a main constituent of the tissues of the mesoblast, just as 

 characteristically as it is by the epiblast. 



The microscopic structure of the entosteruite of Limulus is 

 essentially as follows : — a firm, homogeneous, or sparsely fibril- 

 lated matrix in which are embedded nucleated cells, generally 



Tlie formation of grape sugar from chitin under the above treatment wiih 

 sulphuric acid is characteristic, but the evidence of its presence I could get 

 with the small amount of dry material available vras but feeble, and I am not 

 prepared to say positively that the substance is ' chitin,' or even that it is 

 chiefly chitin; but considering its solubilities, or rather insolubilities, it is 

 probably either that substance or a mixture of that and a substance allied to 

 keratin. There is also -the possibility to be taken into account that it is a 

 material hitherto undescribed of the same nature as chitin, but differing from 

 it in certain minor particulars : it would, however, be necessary to get it very 

 pure and in some quantity to make the investigation of any value." 



