134 THF 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 
hemalum-eosin the hard cartilage stains red, the soft blue; and he 
points out that even with over-staining by hemalum 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 hetween 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- 
quently we cannot be said to possess any really exhaustive and 
