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 part 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. 8. 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 Michigan. 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 material 
