HEREDITY 197 



has two symmetrically placed eyes. The development of the anterior 

 cell contrasts sharply with that of the posterior. This embryo like- 

 wise produces a prototroch and a pre-trochal region, with an apical 

 organ, but produces no post-trochal region, develops no trunk or setae, 

 and does not become metameric. Except for the presence of an apical 

 organ, these anterior embryos are similar in their general features to 

 the corresponding ones obtained in Dentaliiim. None of the indi- 

 viduals observed developed a definite eye, though one of them bore a 

 somewhat vague pigment spot. 



"This result shows that from the beginning of development the mate- 

 rial for the trunk region is mainly localized in the posterior cell ; and, 

 furthermore, that this material is essential for the development of the 

 metameric structure. The development of this animal is, therefore, 

 to this extent, at least, a mosaic work from the first cleavage onward 

 - a result that is exactly parallel to that which I earlier reached in 

 Dental ium, where I was able to show that the posterior cell contains 

 the material for the mesoblast, the foot, and the shell; while the ante- 

 rior cell lacks this material. I did not succeed in determining whether, 

 as in Dentalium, this early localization in Lanice preexists in the un- 

 segmented egg. The fact that the larva from the posterior cell develops 

 but a single eye, suggests the possibility that each of the first two cells 

 may be already specified for the formation of one eye; but this inter- 

 pretation remains doubtful from the fact that the larva from the ante- 

 rior cell did not, in the five or six cases observed, produce any eye." 

 It should, however, be pointed out that the posterior cell, which 

 in the whole egg only seems to form the segmented trunk of the 

 animal, forms a head if isolated, although the latter in the cases 

 thus far observed was not symmetrical. We do not wish to enter 

 further into this field of experimental embryology, and we refer the 

 reader, in addition to the papers mentioned here, to those published by 

 Chabry, Conklin, Driesch, O. Hertwig, Morgan, Pfliiger, Roux, Schultze, 

 Whitman, Wilson, and many others. It was our intention in this 

 connection only to show that the first structures in the egg do not seem 

 to be beyond the reach of purely physicochemical data. On the other 

 hand, these data corroborate still further the statement that the early 

 forms of the embryo are determined by the egg, and in no way depend 

 upon the spermatozoon. It has occasionally been suggested that it 

 might be possible to produce an organism from a spermatozoon alone, 

 if the latter were only transplanted into a nutritive medium. This 

 could only be true if the culture medium used possessed also the typical 

 structure of the egg, which is not very likely. 



Boveri and others have shown that often very early in the develop- 



