^20 JORDAN. [Vol. VIII. 



cleavage. The total absence of any regularity in the arrange- 

 ment of the cells is the most conspicuous feature. 



It cannot reasonably be held, I think, that these eggs depart 

 from the "normal" or the "type." They fairly represent the 

 average and common course of cleavage in the newt, and would 

 undoubtedly have resulted in normal development. I am con- 

 vinced of the truth of this latter assertion through careful 

 following out of a large number of living eggs. 



The difficulty of following the cleavage in the Qgg of the 

 newt is much enhanced by the opacity of the enveloping mem- 

 brane. I have, therefore, usually removed the ^%g from the 

 membrane soon after deposition. The removal of the membrane 

 is accomplished with sharp needles and fine scissors, but is 

 attended with considerable difficulty, and often results, even 

 with the best of care, in the destruction of the egg. I have 

 succeeded, however, after some practice, in extricating without 

 injury a number of eggs and in following their subsequent 

 development. 



Figs. 33A-33F illustrate successive stages in the develop- 

 ment of a living Qgg. Fig. 33 A shows the upper pole at the 

 beginning of the third set of cleavage furrows. These furrows 

 appeared in this egg at the time when the "equatorial" plane 

 was normally due, and must hence be regarded as " homologous " 

 with the usual "first equatorial plane" of the amphibian tgg. 

 Fig. 33B is taken ten minutes later and exhibits an interesting 

 and remarkable bilaterality. The two furrows on the left have 

 united near the equator of the ^g'g, and, except for the unusual 

 nearness of their proximal ends to the middle of the upper 

 pole, would be regarded as part of a typical equatorial. The 

 two furrows in the right half of the egg, on the contrary, cut 

 down to a point near the middle of the lower pole, as is shown 

 by the aid of an underlying plane mirror (Fig. 33C). By 

 comparison of these views of the upper and lower poles it is 

 clearly seen that in one half of this cigg the tJiird cleavage 

 plane is an undoubted vertical, while in the other half it is a 

 dubious equatorial. The fourth rhythmical nuclear division 

 cleaves the ^gg into the cells seen in Fig. 3 3D. Comparison 

 with Fig. 33C will show the distortion of the earlier cleavage 



