134 THE ORIGIN OF VERTEBRATES 



staining (Fig. 57). In the case of the soft cartilage the capsular 

 substance stains respectively a brilliant red or blue, while that of 

 the hard cartilage is coloured a deep yellow, so that the junction 

 between the parachordals and the branchial cartilages is beautifully 

 marked out. Then, again, with thionin, which gives so marked a 

 reaction in the case of the soft cartilage, the hard cartilage of the 

 auditory capsule is not stained at all, and in the trabecule the deep 

 purple colour is confined to the mucoid cement-substance between 

 the capsules, just as Schaffer has stated. The same kinds of reactions 

 have been described by Schaffer: thus by double staining with 

 hrenialum-eosin the hard cartilage stains red, the soft blue ; and he 

 points out that even with over-staining by haemalum the auditory 

 capsule remains colourless, just as I have noticed with thionin. He 

 infers, precisely as I have done from the thionin reaction, that 

 chondro-mucoid, which is so marked a constituent of the soft cartilage 

 and of the muco-cartilage, is absent or present in but slight quantities 

 in the hard cartilage. Similarly, he points out that double staining 

 with tropceolin-methyl- violet stains the hard cartilage a bright orange 

 colour, and the soft cartilage a violet. 



The evidence, then, shows clearly that a marked chemical differ- 

 ence exists between these two cartilages, which may be expressed by 

 saying that the one contains very largely a basophil substance, 

 which we may speak of as belonging to the class of chondro-mucoid 

 substances, while the other contains mainly an oxyphil substance, 

 probably a chondro-gelatine substance. 



We may perhaps go further and attribute this difference of 

 composition to a difference of origin ; for whereas the soft cartilage 

 is invariably formed in a special tissue, the muco-cartilage, which 

 shows by its reaction how largely it is composed of a mucoid sub- 

 stance, the hard cartilage is certainly, in the case of the cartilage of 

 the cranium where its origin has been clearly made out, formed in 

 the membranous tissue of the cranium of Ammoccetes — i.e. in a 

 tissue which stains light blue with thionin, and contains a gelatinous 

 rather than a mucoid substratum. 



The best opportunity of finding out the mode of origin of the 

 hard cartilage is afforded at the time of transformation, when so 

 much of this kind of cartilage is formed anew. Unfortunately, it 

 is very difficult to obtain the early transformation stages, conse- 

 cpuently we cannot be said to possess any really exhaustive and 



