EMBRYOLOGY OF CRYPTOBRANCHUS ALLEGHENIENSIS. 159 



It is not known whether the eggs of a given spawning are all 

 fertilized at the same time, hence some of the diversity in the 

 time of appearance of the first cleavage furrow may be due to a 

 difference in the time of fertilization. 



The first cleavage furrow begins as a pit, which gradually 

 elongates, rapidly at first then more slowly. The point of origin 

 of the first cleavage furrow remains always uppermost, even 

 though the envelope is rotated. 



B. The Second Cleavage Furrow. This furrow makes its 

 appearance about six hours after the first, which by this time has 

 extended over about half the distance to the equator of the egg. 

 The second cleavage furrow usually cuts the first at right angles, 

 but some variations from this procedure are shown in the figures. 

 (See Figs. 4-7.) 



Some time before the appearance of the second groove, the 

 first one appears constricted and narrow in the middle portion, 

 while still broad at the ends. The earliest indication of the 

 second furrow is usually a roughness in the region where the 

 second groove is to intersect the first. The appearance of 

 " Faltenkranzen " a quivering of the surface with the forma- 

 tion of fine radiating or parallel wrinkles, which extend outward 

 from the cleavage furrow for a moment, tremble, and disappear 



a common phenomenon in the cleavage of the amphibian egg, 

 is quite marked at the time of the beginning of the second cleav- 

 age furrow. For some time after its appearance the second fur- 

 row is much broader, though of course shallower, than the first. 



C. The Third Cleavage Furrow (see Figs. 8-12). These fur- 

 rows mark the establishment of the 8-cell stage about four or five 

 hours after the appearance of the second cleavage groove. Hence 

 the third division is more rapid than the second. At the time 

 when the third furrows are initiated the first furrow has usually 

 reached or passed the equator ; the second one is confined to the 

 upper hemisphere. 



The third cleavage furrows ordinarily begin as two pits in the 

 first furrow, not far from its point of intersection with the second 



the center of the animal pole of the egg and equidistant 

 from that point. From these pits the third furrows proceed in an 

 approximately vertical direction. The third cleavage furrow seldom 



