Experimental Studies on Germinal Localization. 243 



in some cases distinctly show a few small cells lying between the 

 gut and the ectoblast. The only conclusion that I am justified in 

 drawing is that the mesoblast cells are more numerous in the CD 

 larva than in the AB, and additional material will be necessary 

 to determine the point. When, however, we consider the evi- 

 dence, not entirely conclusive but still fairly definite, given in my 

 preceding paper, that the material of the polar lobe (which 

 passes only into the CD half) is necessary for the production of 

 the coelomesoblast, I think It may be concluded with some prob- 

 ability that the mesoblast-cells (If they be such) found in the AB 

 half represent a portion of the larval mesoblast or ectomesoblast, 

 and that the coelomesoblast Is represented only in the CD half. 

 I hope in the near future to obtain additional material that may 

 afford a more definite conclusion. 



IV. SUMMARY. 



{This Applies Primarily to Patella.) 



1. Isolated blastomeres of any stage segment essentially in 

 the same manner as if still forming part of a complete embryo, 

 with a tendency, however, for all unequal divisions to be less un- 

 equal than In the normal. The partial form of cleavage is fre- 

 quently masked by shifting of the cells. 



2. All of the partial embryos, if of sufficient size, tend to close 

 to form morula- or blastula-like structures ; but these only gastru- 

 late if they contain entoblast material from the basal cells. Apart 

 from such closure all of the cells, and their products, as far as 

 examined, differentiate typically, regardless of their relative po- 

 sition or of complete Isolation from their fellows. 



3. Isolated >^-mIcromeres produce pyriform larvs, bearing 

 at one end an apical organ, at the other a group of four primary 

 and two secondary trochoblasts. In Dentalium the apical organ 

 is produced only by the posterior micromere, id. 



4. Isolated primary trochoblasts (i') divide twice and pro- 

 duce four typical ciliated prototrochal cells. Isolated first prod- 

 ucts of the primary trochoblasts (i"S i"'") divide once and pro- 



