264 BAUR, ON CH1TINE. 



of wheat-starch, whose diameter does not exceed -0336 mm., 

 if they really existed in the atmosphere in sufficient quantity 

 to explain the generation of Infusoria, Avhose apparition 

 astonishes and stupifies us, should have been immediately 

 discovered in the same situations, and far more easily even, 

 than the starch-grains, seeing that they ought to exist in 

 much greater numbers. To a negation of this kind, in the 

 actual state of science, but one answer is possible — show 

 these ova. 



On Chitine. By M. A. Baur. 



In 'Reichert's Archiv' for I860, part 1, M. A. Baur 

 has published an interesting memoir on the chitinous tendons 

 of Articulata, and their relation to the change of skin. 

 The simplest and oldest view of these structures regarded 

 them as being nothing more than inward prolongations of 

 the outer skeleton, resembling true tendons, but not as 

 corresponding to those of the Vertebrata, which consist 

 of connective tissue. Leydig, on the other hand, considers 

 that these tissues do correspond to one another, and that, 

 while the tendons of Vertebrata often become bony, those 

 of Articulata tend to change themselves into chitine. 



If, indeed, as has been supposed to be the case, the chitine 

 and connective tissue of the tendons are in continuous 

 connexion, and pass gradually into one another, then we 

 should be forced to consider them as nearly allied, and that 

 chitine is, in fact, a modification of connective tissue. 



This view of the question is maintained by Leydig, but on 

 the other hand is opposed by Hackel and Kolliker, accord- 

 ing to whom the chitine of the Articulata is a laminated 

 secretion of the epithelial cellular layer. The external chitine 

 is known to be continuous with the intima of the intestinal 

 canal, and this latter is admitted by Leydig to be a secretion 

 of the epithelium. The theory supported by Hackel and 

 Kolliker has, therefore, this advantage, that it does not 

 disunite structures which are histologically identical, but 

 considers the whole chitine skeleton of the Articulata from 

 one point of view. If, however, it is correct, then it 

 becomes a general characteristic of chitine that it always 

 forms the boundary of free surfaces, or the lining of those 

 that are turned inwards. 



