No. 2.] ORGANIZATION OF THE EGG OF UNIO. 267 



by this, and it is necessary to sharply separate these in our 

 thinking, if not in our vocabulary. In the first place is meant 

 the distinction that is marked by the appearance of the *' polar " 

 globule at a point {i.e., " pole ") on the surface ; in the second 

 place is meant the distinction that is based on the existence of 

 ectodermal and entodermal portions of the blastula or gastrula. 

 Now formation of polar globules is historically a very different 

 thing from embryo formation, and there is no other reason for 

 assuming that the axes marked out by these distinct processes 

 m!isi correspond, than that apparently they almost always do. 

 Therefore I fail to see why such observations as those of Wil- 

 son and Ziegler furnish evidence against such an organization 

 of the egg-cytoplasm as we have maintained. If there be an 

 ectental orientation of the egg-cytoplasm prior to maturation, 

 it would be natural to expect a control of the place of polar 

 globule formation by this, of such a sort that the polar globules 

 would tend to arise at the ectodermal (animal) pole, as is usu- 

 ally the case, or entodermal (vegetative) pole, as happens appar- 

 ently in the Ascidian egg (Castle). But one can readily imagine 

 that other forces might operate more powerfully and determine 

 a different location of the polar globules. 



Just as little do I consider that observations of the develop- 

 ment of the egg under pressure or of the development of parts 

 into whole embryos militate against the view here upheld. The 

 eggs, like the adults of many animals, possess great power of 

 reorganization. In such cases the reorganization of the egg- 

 cytoplasm would be a necessary preliminary to typical develop- 

 ment, however we may think of it as taking place. 



Finally, even if it should be proved that the axis of the 

 embryo may be determined either by the point of entry or by 

 the copulation path of the spermatozoon, we should have here 

 no evidence of lack of previous organization in the cytoplasm, 

 but simply another striking confirmation of the wonderful 

 power of reorganization of the egg-cytoplasm, for it has been 

 shown that parts of fertilized eggs in which this process is 

 held to occur (frog, sea-urchin) are capable of typical develop- 

 ment, in which case the path of the spermatozoon can exercise 

 no possible directive influence. 



