THE ORIENTATION OP THE FROg's EGG. 375 



very slight alterations have been made in this portion prepa- 

 ratory to publication. 



II. 



In studying a series of eggs of the early stages of Rana 

 temporaria from the segmentation period to the beginning 

 of the formation of the blastopore, a few points in regard to 

 the peculiar development of the pigment and the orientation 

 of the dorsal lip of the blastopore have been noted, and are 

 here given briefly. 



The eggs, which had been previously hardened and preserved 

 in 80 per cent, alcohol, were studied chiefly by surface views 

 with a dissecting microscope. The study of the segmentation 

 of the early stages only verified previous accounts. The first 

 cleavage furrow divided the egg into two equal parts ; the 

 second is at right angles to it ; the third or horizontal furrow 

 is much nearer the upper or pigmented pole, thus forming four 

 small pigmented cells iu the upper and four large cells in the 

 lower hemisphere.^ The four cells of the upper half then 

 each divide, thus forming eight cells ; but the division from 

 this point becomes quite irregular, both in the upper and lower 

 halves of the egg. I found a number of eggs in what clearly 

 seemed a twenty-four cell stage — eight cells in the lower and 

 sixteen in the upper j but I could not verify the fact iu the 

 living egg. 



A curiously abnormal egg of eight cells was found where the 

 horizontal or third furrow was entirely wanting, and the fur- 

 rows of the next division, which would normally have divided 

 the egg into sixteen cells, had cut through from the upper 

 pole, reaching down about two thirds of the distance to the 

 lower pole. On sectioning the egg eight nuclei were found 

 corresponding to the number of segmentation furrows. No 



^ I have found a number of probably abnormal eggs from one lot in which 

 the first furrow divided the egg into unequal parts, one large and the other 

 much smaller. Also a number of eggs of the four-cell stage, where neither 

 the first nor second furrow had met at the lower pole. 



