22 NERVE COMPONENTS OF BONY FISHES. 



but less specialized than the last. I do not look upon 

 them as aberrant." My studies fully confirm the central 

 position given to Menidia, for the nervous system exhibits 

 in many of its most fundamental features the characters 

 of a generalized type ; nevertheless it is in many minor 

 respects very highly specialized, these modifications in 

 the nervous system being largely correlated with the 

 exaggerated development of the organs of special sense, 

 notably the eye and the ear. 



I have studied both of these species somewhat and, so 

 far as I know, there is no essential difference between 

 them. The figures and descriptions are all based upon 

 sections of Menidia gracilis. Probably they apply to 

 both equally well. 



The most essential condition of success in researches 

 on the nerve components is the preparation of perfect 

 serial sections. The series must be unbroken and the 

 medullary sheaths must be perfectly preserved, for it is 

 upon the characters of the latter that we must depend 

 very largely to distinguish the components in the periph- 

 eral courses of the nerves. The animal chosen should be 

 small enough to be cut whole or nearly so and should be 

 adult or practically full grown in order that the medullary 

 sheaths may be fully laid down. The latter point is not 

 necessary, but it is certainly a great advantage. I have 

 found, as many before me have done, that the teleostean 

 tissues are refractory to a surprising degree; standard 

 methods which work perfectly with amphibian or 

 selachian material fail utterly here. Different species 

 of teleosts, moreover, vary somewhat in their reactions 

 to stains. 



The necessity for very thorough decalcification of 

 course complicates the problem greatly. In general, 



