No. 2.] EARLY DEVELOPMENT OF AMBLYSTOMA. 36 1 



elude with Hallez ('86) that " chaque element histologique 

 poss^de, lui aussi, ces deux polarites de I'animal, polarites qui 

 persisteraient dans la cellule-oeuf, apr^s qu'elle a cesse de faire 

 partie des tissus maternels." 



Relation of ovic axis and embryo to cleavage planes. — One 

 of the first questions to be considered is the relation of the 

 first furrow to the ovic axis, the upper pole of which is marked 

 by the point of exit of the polar bodies. 



Schultze ('87) holds that the plane of the first furrow is deter- 

 mined by the ovic axis and the eccentric germinal vesicle, and 

 that its direction may be anticipated in the unsegmented egg. 



Roux ('88), on the other hand, maintains that the first cleav- 

 age is determined by the ovic axis and the path of the male 

 pronucleus, as first stated by Newport in 1853. 



In Amblystoma, Petromyzon, and Coregonus this furrow 

 does not always pass through the ovic axis, nor does it bear 

 a constant relation to it, except that it generally passes in a 

 plane parallel. 



This peculiarity Rauber ('83) has noted, and suggests that 

 there must be a " Polflucht " through the influence of which 

 the furrows are thrown away. Whether this be accepted or 

 not the fact remains, and is of great importance, that this ec- 

 centricity commonly occurs, hence the ovic axis cannot be 

 considered as a rigidly determining factor. 



Concerning the relation of the succeeding furrows to the 

 first, it seems conclusively shown from the variations recorded 

 in the preceding pages, as well as the observations of Rauber 

 ('83) and Jordan and myself ('94), that in the forms studied no 

 fixed relation exists. 



Another theoretically important question is the relation of 

 cleavage furrows to the axes of the embryo. 



Newport, in 1853, called attention to this in the following 

 words : " I have long been aware that the axis of the embryo 

 was in line of the first cleft of the yolk." In a following para- 

 graph, however, the author states : " The observations point out 

 that at times the axis deviates to the right or left of the line." 



From a number of experiments Roux, in 1883, reached the 

 following conclusion : " Mit der Ebene der ersten Furchung 



