4()S J. DUESBERG 



Irrospoctive of the fixative employed, one may notice in 

 Fundulus embryos as young as two days, that occasionally and 

 quite independently of the penetration of the fixative, the 

 chondriosomes in the different tissues are not equally well pre- 

 ser\'ed. I have repeatedly found, for instance, that the chon- 

 driosomes of the intestinal epithelium, or of the blood-corpuscles, 

 were well fixed, when no chondriosomes at all could be seen in 

 the neighboring cells. I should consider this an indication that, 

 already in these early stages, a differentiation of the chondrio- 

 somal substance has taken place in the different tissues. It was 

 found furthermore that some difference in the chondriosomes 

 exists between the posterior and the anterior part of an embryo 

 (as also between the regenerated and the regenerating part of the 

 tail of a triton), as it very often appeared necessary to carry the 

 differentiation of the stain to different degrees depending on the 

 part desired for study. 



Besides a few trials on Fundulus with a vital dye, Janus- 

 green, which gave successful stains only in the epidermic cells 

 (these experiments were, however, not carried very far), three 

 stains were resorted to, — iron-haematoxylin, Benda's sulfali- 

 zarin-crystall-violett and acid fuchsin-methylgreen. The first 

 named gives occasionally very good preparations. The second 

 one gave no useful preparations whatever when applied after 

 Regaud's fixation, and only very few good ones (two or three on 

 some 150 embryos) with the material fixed in any of the chrom- 

 osmic mixtures mentioned above. A similar experience was 

 met with when it was attempted to stain the testicle of a fish, 

 after fixation in Benda's fluid. These technical difficulties were 

 not due to the staining reagents, for the same set, applied to a 

 familiar object (the mammalian testicle) worked perfectly; it 

 was finally discovered that nothing was wrong with the material 

 either, for, to my great surprise, acid fuchsin-methylgreen gave 

 excellent preparations. From this, two conclusions may be 

 drawn, interesting enough, in my opinion, to justify this narra- 

 tion of my experience: the first one is that on a given material, 

 one chondriosomal stain may give satisfactory preparations 

 when the other does not ; and the second one, still however 



