Localization of the Nemertinc Egg. 



321 



Fig. 19 (x2i6). 



LarvcE Developed from Blastula Fragments. 



A, larva (age 351^^ hours) from a fragment (1^:2/3 of blastula) ; direction 

 of cut is not known. B, larva (age 3514 hours) from upper or lower half of 

 blastula. Note presence of both enteron and apical organ. C, larva (age3r48 

 hours) from the upper 2/3 of blastula. Note presence of both enteron and 

 apical organ. 



size, was the only one alive thirty-five and a half hours after fer- 

 tilization. Its cilia were waving, but there was no motion of the 

 animal as a whole. The body is spherical, with a large solid en- 

 teron nearly filling the cavity of the blastocoele. The chief defect 

 is in the absence of the apical organ, as it is too early (35/^ 

 hours) for the lappets to appear (Fig. 19A). The direction of 

 the cut is not known and the defect, therefore, cannot be corre- 

 lated with any definite portion of the blastula. 



The experiments on blastulae give only one organ which can be 

 considered as definitely specialized. The apical plate is developed 

 in each of two embryos from the upper two-thirds of a blastula, 

 while it is absent in those developed from the lower one-third. 

 No explanation can be given of the apparently greater regulative 



