CHONDRIOSOMES IN CELLS OF FISH-EMBRYOS 471 



as is the periblast, remarkably rich in mitochondria. This tact 

 accounts undoubtedly for the special coloration of these cells, — 

 a phenomenon which students of the segmentation of the fish- 

 egg have mentioned; Agassiz and Whitman ('84) have already 

 described, in Ctenolabrus, differences between the staining prop- 

 erties of the central and the marginal cells, and later Kopsch 

 ('01) expressly mentioned a ''dunklere Fiirbung der Randseg- 

 mente" in Belone acus. 



Figure 1 represents a cross-section (the 37th, — 5 n thick — 

 from the posterior extremity) of an embryo of Fundulus, fixed 

 in Regaud (lot 38) and stained with acid fuchsin-methylgreen. 

 The embryos of this lot were fixed three days after fertilization 

 but are perhaps, judging by the rather scarce data I could find 

 in the literature, somewhat more advanced than the average; 

 I counted in them 28-30 somites and the Kupffer's vesicle had 

 disappeared.^ Figure 1 shows the epiderm, the nervous sys- 

 tem, the somites, the chorda, a blood-vessel with a few blood- 

 corpuscles and the periblastic layer (unfortunately broken in one 

 place) with its nuclei and two pigment-cells. A very marked 

 change has taken place in the structure of the cells. Few mito- 

 chondria and more numerous chondrioconts are found now, and 

 the same holds true throughout the whole embryo, the end-bud 

 included. On the whole, from the cytological standpoint, such 

 a preparation resembles very closely similar preparations of 

 chiek-embryos of about the same age; there are perhaps (but 

 this is a detail of minor importance) a larger number of loops 

 and circles in the fish-embryo. These circles are not to be con- 

 fused with the vesicles found in poorly fixed objects. Owing to 

 the lack of material, I cannot tell how this change took place; 

 I am unable to decide whether these rods were formed by mere 

 elongation of the mitochondria observed in the blastomeres, or 

 by fusion of these granules, as I have found in the rabbit- 

 embryo ('10, 1). 



I come now to a somewhat more detailed description of the 

 chondriosomes in the different tissues. 



1 Shrinkage due to the action of Regaud's fluid might however, be responsible 

 for this. 



