BAUR, ON CHITINE. 265 



To this law, however, chitinous tendons must, according 

 to the ordinary opinion, form an exception, since in them 

 the chitine forms a solid substance, and is continuous 

 with connective tissue. An epithelial secretion and con- 

 nective tissue cannot, however, possibly be continuous with 

 one another, since they must, at least, be separated by the 

 epithelial layer to which the former owes its existence. If, 

 therefore, chitine is the secretion of an epithelial layer, 

 the tendons may pass into it, or may pass into the connective 

 tissue, but assuredly not into both. In the first case 

 the apparent chitine of the tendon is really a process of 

 the outer skeleton ; in the latter it is true connective tissue. 

 Hackel endeavours to prove the latter of these two alterna- 

 tives, considering that the chitine of chitinous tendons pos- 

 sesses neither the fine canals nor the cell-impressions which 

 are found in true chitine. According to Leydig, on the 

 contrary, chitinous tendons prove that ordinary chitine 

 is, in fact, a modification of connective tissue. 



The controversy may be reduced to the following questions : 

 — Are the chitinous tendons continuous with the outer skeleton 

 only, with the connective tissue only, or do they pass 

 insensibly into both? In the first case the tendon is a 

 continuation of the outer integument, in the second it is 

 composed of modified connective, and in the third case the 

 chitinous outer skin must itself be regarded as an abnormal 

 form of connective tissue. 



In the ordinary state of the tissues these problems are 

 difficult of solution, but they become comparatively easy 

 if we examine an animal at the time of moulting. It is 

 well known that the tendons are cast with the skin. If 

 one takes a crayfish which is just about to moult, we shall 

 find the soft new skin lying under the hard old one : if we 

 now isolate the mandibular muscle, so that on the one side 

 it is attached to the back of the cephalothorax, while on 

 the other its tendon is united to the mandible ; and if we 

 remove from the latter its old chitinous covering, which 

 can generally be effected without much difficulty, the 

 chitinous tendon will come away also. The muscle does 

 not, however, thereby lose its attachment to the tendon, but 

 as under the old, hard skin of the mandible, a new and soft 

 one is formed, so also, instead of the old tendon, we find a 

 new tendon, which is attached to the new mandible. The 

 new tendon resembles the old one in form and sculpture, 

 but it differs from it in consistence ; and also in this, that, 

 while the old tendon is apparently solid, the new one is 

 distinctly tubular — and, in fact, the old tendon lies in the 



