The Common Leopard Frog 



kind, we can see something more of the marvellous changes 

 that have begun and will continue from the vital force of the 

 life within until the egg has become a frog in miniature. If 

 we examine the eggs with a lens very soon after they are laid, 

 we can see that a groove appears in the midline at the top of 

 each. It increases in length until it encircles the egg. The 

 partition of which this is the external evidence divides the egg 

 into two equal parts. (Fig. 202.) Many scientists believe that 

 these correspond to what will be the right and the left side of the 

 young frog. This groove is visible to the naked eye, though 

 somewhat difficult to see. A second groove appears at right 

 angles to the first and rapidly encircles the egg until the latter is 

 divided into four nearly equal parts. (Fig. 203.) The next 

 division is made by a horizontal partition instead of a verti- 

 cal. This partition and its external groove are somewhat 

 above the centre of the egg, so that the upper portion is smaller 

 than the lower. From this time on the division is more rapid 

 and more irregular. It is possible to follow it somewhat 

 farther with just a hand-lens, but soon the parts (cells) be- 

 come too small and too many to be distinguished. (Fig. 204.) 



Fig. 204. Series of diagrams to show cleavage of the frog's egg. The second 

 very nearly corresponds to Fig. 202. The third represents Fig. 203. The last is a 

 stage just preceding that of Fig. 205, in which the cells are too small to be seen. 

 (After Ecker.) 



If we look carefully at the eggs on the afternoon of the 

 second day after they are laid, we shall see a dark line of crescent 

 shape' on one side, just below the middle (equator). (Fig. 205.) 

 Twelve hours later the crescent has become a circle. The black 



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