No. I.] SPERMATOGENESIS OF BATRACHOSEPS. 5 



these fixatives some of the interiorly situated cells gave fairly 

 good images, yet it was readily seen that the cytoplasm of the 

 cell had become greatly contracted and distorted, to such an 

 extent as to represent no more the true structure of the cell. 

 It is comparatively easy to fix chromosomes and spindles, more 

 difficult to fix the cytoplasm and the linin. Osmium-chloride 

 is in many respects a most valuable fixative, especially in solu- 

 tions of from one-half to one-tenth per cent, but it always pos- 

 sesses the undesirable quality of blackening the tissue, though 

 in a lesser degree than osmic acid. I have, however, no 

 doubt that this chemical will be found very useful for fixing 

 several kinds of tissue, especially in connection with potassium- 

 bichromate, when it allows of intense staining and detailed 

 differentiation. The fixative on which I finally decided as 

 giving the most satisfactory results, as regards the fixation of 

 the testes of Batrachoseps, is a mixture of iridium-chloride- 

 acetic, according to the formula published in the Zeitschrift f. 

 wiss. Mikr., Bd. XIV, pp. 195-202. The time of fixation is 

 from three to twelve hours, though I think that the best 

 results were had with the shorter time. There is no percep- 

 tible shrinkage of the tissue, no blackening of the cells, and the 

 outer rows of cells are as perfectly fixed as those in the center. 

 After fixation the testes were washed in tap water for about 

 one hour, then passed through the alcohols. For clearing, ber- 

 gamot oil was found most suitable, but it was followed by xylol, 

 which latter was again displaced by bergamot before imbed- 

 ding in parailEin. The sections were cut in paraffin of 54 Fahr. 

 melting point, and from 4 to 6^6 thick, each cell being cut in 

 from two to three parts. This latter is of importance because 

 cells which are not cut into do not stain properly, making 

 it impossible to study the finer structures of the cell. The 

 sections were then fixed to the slide by the alcohol method 

 as described in Bd. XIV, Zeitschr. f. wiss. Mikr. (1897), 

 pp. 195-202. 



Stains. 



The majority of the sections were stained by the Benda iron- 

 haematoxylin method, and after-stained with congo. Another 



