92 ME. W. a. EIDEWOOD ON THE HTOBEATfCHIAL 



that render it so aberrant appear only during and after meta- 

 morphosis. This is of course the conclusion one would expect 

 to arrive at ; but hypotheses, conjectures, and arguments are 

 of infinitesimal value compared with ocular demonstration of fact. 

 Concerning the methods adopted in this portion of the research, 

 extensive preliminary trials were made on the tadpoles of the 

 common frog and of Alytes, with a view to discovering the method 

 which would demonstrate the facts in the most intelligible 

 manner, and yet leave the skeleton in a condition in which it 

 may be preserved for subsequent examination. The easiest 

 methods of preparation are those which fail to satisfy the second 

 condition. The steeping of the body in water at a temperature 

 of about 80° C, a method largely used for the preparation of the 

 skeleton of Elasmobranch fishes, was rejected at once on account 

 of the shrinkage and distortion which it occasions. Putrefactive 

 maceration, which may sometimes be employed with advantage 

 in the preparation of cartilaginous skeletons, was found unsatis- 

 factory on account of the tendency which the delicate skeleton 

 showed to fall to pieces, and the possibility of loose cartilages 

 becoming lost or overlooked — objections from which the hot- 

 water method is not free. As I had previously found the method 

 of staining with borax-carmine and clarifying with clove-oil of 

 the greatest value when studying the carpus and tarsus of Anura, 

 larval as well as adult (23), I applied the process to the branchial 

 skeleton ; but had to discard it on account of the resulting 

 brittleness of the tissues. Clarifying by glycerine and caustic 

 potash I also tried ; but the preparations made in this way cannot 

 be kept permanently in the clarifying fluid, since the potash 

 brings about the ultimate disintegration of the cartilages. 

 Parker's method, of staining with an ammoniacal solution of 

 carmine and then steeping in glycerine, is open to less objection 

 than the preceding methods ; but it resembles them all in being 

 inapplicable at the critical period when the cartilages are becoming 

 absorbed, — the most important stage of all. All methods involv- 

 ing clarification and the use of transmitted light fail utterly here. 

 I was therefore forced to fall back on tho very simple expedient 

 of dissecting the parts under a simple microscope by powerful 

 reflected light : a tedious and delicate operation, it is true ; but 

 with fine instruments, combined with a knowledge, to be gained 

 only by experience, of the relative toughness of muscle, peri- 

 chondrium, and cartilage, the difficulties can be overcome. 



