Early Development of Desmognathus Fiisca. 537 



seldom larger, although often smaller. The smaller ones develop as 

 the larger, and as a rule pass through the different stages with greater 

 rapidity. Freshly laid unsegmented eggs seem to be unifoinnly white 

 with no polar differentiation, but when very closely examined it is 

 found that the pole of the egg which floats up is of a pure chalky- 

 white while the opposite pole and about two-thirds of the egg nearest 

 it, although white, has a slight yellowish tinge. This lighter polar 

 cap is somewhat variable and its limits are not well defined. It may 

 be noticed in the living eggs, but it is more apparent in preserved 

 ones. The lighter polar cap marks the position of the animal pole 

 or region of more purely formative yolk. In microscopical section 

 the only difference which could be observed between the two areas 

 of the egg before segmentation was the smaller yolk granules of the 

 animal pole. 



In a study of segmentation stages, my results agree for the most 

 part with the various cleavage stages described by Wilder in Feb- 

 ruary, 1904. 



In a large number of eggs collected from widely separated places 

 during several years, I have only found a few which exhibited so 

 regular a type of cleavage as described in Wilder's eight-cell and 

 later stages. Even as early as the four-cell stage the irregularity in 

 cleavage was considerable. These eggs seemed to be perfectly normal, 

 for in many eases very irregularly segmented eggs developed into 

 perfectly usual later embryos. Another marked difference found in 

 the specimens which I studied, was that in the early stages 

 the segmentation planes were much slower in making themselves 

 evident at the lower pole than seems to be the case in those studied 

 by Wilder. The eggs which came under my notice seemed in both 

 of these respects more like those of Cryptobranchus as described by 

 Bertram G. Smith in August, 1906. 



Surface views alone do not seem to show all the important divi- 

 sions of the egg even in early stages and little idea can be gained of 

 how deep the cleavages have penetrated unless sections are made. A 

 complete division of the egg into entirely separate blastomeres was 

 not accomplished until a rather late morula stage was reached. 



From 21/0 to 3 hours after the eggs are laid the first indication of 



