BA'.R, ON CHITINE. .^G? 



portions of the general integument. 2dly. That the tendon is 

 composed of the same layers as the skin, but with an inverted, 

 concentric arrangement. Thus the external chitine of the 

 outer skin is continuous with the inner chitine skeleton of the 

 tendon, the lower connective-tissue layer of the skin with 

 the connective-tissue sheath of the tendon, and this only is 

 immediately connected with the connective tissue of the 

 muscle. 3dly. The chitinous skeleton of the tendon is cast 

 with the skin at every moult ; and this is true, not only of 

 the main stem, but also of its finest branchlets. 4thly. Con- 

 tinuity between chitine and connective tissue never occurs 

 but in the finest branches of the tendons, as everywhere else 

 they are separated by a layer which secretes the chitine. 

 5thly. The chitine of the tendons does not in reality differ 

 from that of the general integument ; the apparently fibrous 

 condition, and the longitudinal striation, and the capability of 

 being split, all arise from the folding of the homogeneous 

 lamellae, which takes place after the removal of the old 

 tendon, and when the young chitine has already attained a 

 certain degree of hardness. 



The chitine of the tendons forms therefore no exception to 

 the general rule, that this structure occurs only as a cover- 

 ing of free surfaces ; and the chitinous tendons can no longer 

 be relied on as a proof of the connexion which has been sup- 

 posed to exist between chitine and connective tissue. Since, 

 however, the chitine of tendons possesses no pores, nor any 

 cell-like impressions, these conditions can no longer be re- 

 garded as necessary to true chitine, and the characteristics of 

 chitine are therefore reduced to these, that it bounds sur- 

 faces, consists of a variable number of homogeneous lamella;, 

 possesses a certain power of resisting chemical agents, and is 

 constantly accompanied by a soft and thin layer, consisting of 

 a simple series of nuclei connected together by a molecular 

 substance. Taking it therefore for proved that chitine is not 

 to be regarded as a form of connective tissue, M. Baur con- 

 cludes his memoir by considering in what manner it is pro- 

 duced by the chitinogenous layer. This might be effected in 

 two ways ; either this layer might be changed into chitine, in 

 which case it must be regarded as an immature form of chi- 

 tine ; or the chitine might be directly produced by the 

 chitinogenous layer. In the first of these cases, however, 

 we ought to find layers in every intermediate state between 

 chitinogenous tissue and true chitine, which is by no means 

 the case. On the contrary, even the youngest lamella? are 

 true chitine, and show no resemblance to the chitinogenous 

 laver. 



