348 EYCLESHYMER. [Vol. X. 



The superior pole some hours later (Fig. 3) shows no trace 

 of the saucer-shaped depression. The pit at its center has 

 elongated as indicated in Figs. 3 and 4. In the meantime a 

 second polar body has appeared. The elongation or slit-like 

 extension of the pit was also observed in the eggs of Rana. 



I have sectioned a number of eggs at this stage to determine 

 what relation, if any, the pigmented path of the spermatozoon 

 bears to this slit, but no fixed relation has been discovered. 



In eggs where the pigment is eccentric I have likewise 

 endeavored to determine what relation a line drawn through 

 the centers of the lightest and darkest portions bore to this 

 slit, but efforts in this direction were also fruitless. 



3. Cleavage of Amblystoma.^ 



In the following pages I shall describe the successive stages 

 of a particular Q.gg which presents a fairly typical cleavage, 

 recording in each case the variations most frequently observed 

 in the twenty to thirty living eggs studied ; these variations 

 being confirmed by a study of hardened material. 



The term cleavage, as here used, covers the whole period of 

 cell-formation up to the time of gastrulation. 



First cleavage. — The appearance of the first furrow is fore- 

 shadowed by a flattening at the superior pole, which soon 

 changes to a furrow. The progress of this furrow over the 

 dark hemisphere is rapid and continuous, covering a period of 

 less than 1 5 min. As the furrow passes toward the opposite 

 pole its rate of progress constantly decreases, and it is i hr. and 

 53 min. (Fig. 13) before the entire periphery of the Qgg is en- 

 circled by a continuous furrow (Fig. 5). The furrow is vertical, 

 dividing the ^gg, as a rule, into two nearly equal parts. Although 

 I have often observed the progress of the ends of the furrow, 

 I have never found any indication of an alternate widening and 

 narrowing of the opposite ends as recorded by von Baer ('34). 



An interesting phenomenon which occurs during the progress 

 of the furrows is the formation of the so-called " Faltenkranzen." 

 Whether they are to be regarded with Reichert ('4i) and others 



1 Some of the facts presented in this portion of the paper are the results of a joint 

 study with Dr. E. O. Jordan ('94). I gladly acknowledge my indebtedness to him. 



