GEEMINAL LOCALIZATION IN THE EGG OF CEREBßATÜLUS. 35 



each larval organ. I am rather inclined to maintain that the 

 mutual relation between two organ bases is somewhat like what 

 Deiesch has expressed with these two terms in the case of the 

 whole egg. This is borne out by the following facts. When a 

 small portion of cytoplasm is cut off from the unsegmented egg, 

 no matter through what plane the section may pass, the effect 

 does not appear on the embryo. Cuts made in one of the 

 blastomeres during the first cleavage or at the 2-cell stage usual- 

 ly do not cause any disturbance in the pilidium. Another still 

 more convincing case is the development of two animal cells and 

 one vegetal cell (2 A+IV) obtained from the 8-cell stage. Here 

 unquestionably the fragment has organ bases of abnormal pro- 

 portions as compared with the normal egg or for instance i-, I-, 

 t-larvœ, yet the resulting pilidium is, so far as my observation 

 goes, entirely free from defects. 



The failure to develop an organ may be due either to a 

 complete lack of its bases or to an insufficient concentration of 

 its basis, if such expression is applicable to the case. There 

 is still another cause which should not be overlooked. This is 

 correlative develojDment. Though I could not determine how 

 important this was is the development of the nemertine egg, yet 

 it is clearly brought out in the case of the ^-larva, in some of 

 which the apical organ fails to develop. Here undoubtedly there 

 is a sufficient amount of the apical organ basis, but the organ 

 itself does not come into existence owing to the disturbance of 

 the mutual relation between neighboring cells {cf. the notochord 

 in the i embryo of Cynthia, Conklin '05 p. 189). 



The other point, on Avhieh I would like to lay special stress, 

 is the regulation in erubryogeny after the blastomeres have been 

 abnormallv disairanged. It has Ions: been known that the normal 



