116 BULLETIN OF THE 



By the study of abundant material from several (ten) different fishes 

 of various ages and sizes, I have endeavored to trace the course of 

 development with sufficient thoroughness to settle the origin of the layer 

 now in dispute, and if possible to throw some light upon the homologies 

 of the scales of the Ganoids. For the most pai't my observations lead 

 me to conclusions in agreement with those of Klaatsch, although in 

 regard to some points I am unable to coincide with his views. 



For the greater part of the material used I am indebted to Dr. 

 Edward L. Mark, who very kindly placed at my service his own supply. 

 These fishes had been reared by him in aquaria from eggs collected at 

 Black Lake, N. Y., in the spring of 1882. They had been killed at inter- 

 vals by various fixing reagents, as indicated in the table following, and 

 carefully preserved in alcohol. The histological conditions were very 

 faithfully preserved in all except one specimen. This, the largest and 

 oldest fish of the lot, had died in the aquarium after attaining an age 

 of fifty-two months and a length of thirty centimeters. When found 

 it could have been dead but a few hours at most, and was at once 

 preserved in alcohol. On studying this fish I found the scales in a 

 most interesting stage of development, but unfortunately the epidermis 

 had so far degenerated that it was impossible to make out anything 

 of importance concerning its relation to the scale. I was moreover some- 

 what apprehensive lest the confinement in which these fishes had been 

 reared, together with the handling and other unnatural treatment to 

 which they had been subjected, might have rendered the conditions of the 

 scales found in this and the other larger fishes abnormal to some extent, 



I was unable to obtain at once healthy material of the proper age to 

 show the later stages of growth, and to this fact is due a considerable 

 delay in the completion and publication of the results of my work. The 

 missing later stages were supplied by material from two young gar-pikes 

 which Mr. S. P. Bartlett of the Illinois State Fish Commission obtained 

 and very kindly sent me. They were killed according to my direction 

 by immersion in strong alcohol, a method that is very satisfactory for 

 epidermal and dermal tissues, and which has the advantage over acid 

 killing-fluids of leaving calcareous structures quite unaffected. For other 

 material which I have studied I am indebted to Prof E. A. Birge of the 

 University of Wisconsin, and through Dr. Mark to Prof. Jacob Reighard 

 of the University of INIichigan. The material from both of these sources 

 had been killed in alcohol. 



To all of these gentlemen I wish to express my gratitude, and 

 especially to Dr. Mark, not only for his liberal supply of materia] 



