Experimental Studies on Germinal Localization. 45 



duced from lower fragments less than half the size of the egg; 

 and that such larva may possess a typical apical organ when the 

 section passes far away from the apical pole; while in no case does 

 the upper fragment produce a larva that ever approaches the 

 normal form. It may therefore safely be concluded that the 

 dwarf trochophores obtained by Yves Delage ('99) arose from 

 fragments including at least a part of the lower polar area. 



The abnormalities observed in larvae from the lower frag- 

 ments range from only slight defects to wholly irregular and 

 monstrous forms, and thus far do not permit any more detailed 

 conclusions regarding the prelocalization than those stated above. 

 A common defect, illustrated by the pair of twins shown in Figs, 

 85, 86, is a more or less imperfect development of the post-trochal 

 region, even when the whole lower area is included in the frag- 

 ment, and sometimes this region appears to be wholly lacking. 

 Much more rarely the apical organ is lacking while the post- 

 trochal region is in greater or less degree developed. Such a 

 case is shown in Fig. 87 (from a preparation), the absence of the 

 apical tuft having been certainly determined in the living larva. 



As in the case of the lobeless larvae, the experiments dem- 

 onstrate that the failure of the upper fragment to produce the 

 missing structures is not due to an insufficient mass of proto- 

 plasm; for I have obtained larvae showing the characteristic de- 

 fects from upper fragments fully two-thirds the bulk of the egg 

 (Fig. 70), and perfect dwarfs from much smaller fragments 

 (Fig. 59). The conclusion is therefore unavoidable that, like 

 the polar lobe to which it gives rise, the lower polar area contains 

 specific materials that are essential for the formation of the apical 

 organ, and of a post-trochal region; and that it is these materials 

 that enter into the formation of the polar lobe, as simple observa- 

 tion of the normal development indicates. 



{b) Fragments obtained by ^vertical section through the axis. 

 — In view of the foregoing results we should expect to find that 

 when the egg is cut exactly vertically, so as to bisect the lower 

 polar area, both fragments should form the polar lobe; and such 

 is in fact the case. The experiments of this type were not very 

 numerous, and only a few cases were obtained In which both frag- 



