MUSEUM OF COMPARATIVE ZOOLOGY. 117 
which it had cost him much time and labor to obtain, but also for his 
direction and many valuable suggestions. 
TABULATED List oF FISHES STUDIED. 
Age. Killing Ate y 
mm, |Months.| Reagent. Condition. Received from 
145 18+ Merkel’s Local aggregations of spongy connective | Dr. Mark. 
fiuid. tissue. 
115 18 HgCl, Bony scale beginning to be formed. Aces 
(hot). 
150 18-+- Merkel’s Spines being formed. paige se 
fluid, 
160 19 90 percent | Few spines. Oy se 
alcohol. 
175 24. Picro-sul- Edges of scale beginning to overlap. Cary ase 
phurie 
acid. 
190 35 2 per cent Mature spines all over scales. RELA PALE 
chromic -+- 
acetic (few 
drops). 
287 ? Alcohol. Spines all over scale ; no ganoin layer. Prof. Birge. 
300 52 Died, 90 per | Epidermis degenerated ; thin ganoin layer. | Dr Mark. 
cent ale, 
300 2 Alcohol, Spines on edges ; thin ganoin layer. Mr S. P Bartlett. 
Alcohol. 
Few spines on edges ; thicker ganoin layer | Prof Reighard. 
The method used has been chiefly the preparation and study of 
series of sections. In all except very young stages it was necessary to 
decalcify the material before it could be sectioned, and even after 
decalcification sections in most cases could not be cut thinner than 
15 p, and often in the later stages it was necessary to make them 
between 20 and 304 thick. For decalcifying I used 90% alcohol to 
which was added a small quantity of 10% hydrochloric acid (in the 
ratio of about 3 to 1). The tissue was usually left in this acid alcohol 
twenty-four hours or more, and then soaked in several changes of fresh 
alcohol to remove all traces of the acid before staining. Sections pre- 
pared by grinding down scales have also been studied, as well as scales 
freed from the soft tissues by treatment with caustic potash. Only by 
the use of the latter reagent was I able to get a satisfactory knowledge 
of the spines which cover the scale in its immature state. 
The stains which have given the best results are Boehmer’s alum 
hematoxylin and Kleinenberg’s hematoxylin. As a nuclear stain the 
