No. 3.] POD ARK E OBSCURA VERRILL. 471 



design. Thus homologous organs, arising in corresponding 

 portions of the embryo (as they naturally would in closely 

 related forms) might arise in exactly the same cell, and cell 

 homologies would appear ; but these homologies are secondary 

 and accidental, and found in no wide range of forms. 



The fact that homologous organs have such a similar mode 

 of origin in the cleavages of annelids and gasteropods, while 

 not proving cell homology, is I think additional evidence in 

 favor of the near relationship of the groups, as indicating not 

 only an homology between corresponding portions of the adult, 

 but between corresponding portions of the embryo as well. 



The proper solution of the problem, it seems to me, lies 

 along the line suggested by Whitman (No. 33,^ c), where he 

 argues that we must regard the developing embryo as a com- 

 plete organism possessed of a definite organization from the 

 very beginning, and that the fact that this becomes split up 

 into more or fewer cells does not affect this complete individu- 

 ality. The embryo, like the adult, is an individual, not a col- 

 lection of individuals, and it is governed by inherent force of 

 its own, not by the mutual interaction of a number of forces. 

 " Organization precedes cell formation and regulates it, not the 

 reverse." " The structure which we see in a cell mosaic is 

 something superadded to organization, not itself the foundation 

 of organization," "The organization of the ^gg is carried 

 forward to the adult as an unbroken physiological unity, or 

 individuality, through all modifications and transformations" 

 (No. 33, c). The difficulties I have pointed out in the way of 

 cell homologies, as well as the facts of post generation in 

 mutilated embryos, seem to me to strengthen this position. 



I believe that, as originally stated by Wilson (No. 34, d), 

 " The fundamental forms of cleavage are primarily due to 

 mechanical conditions, and are only significant morphologically 

 in so far as they have been secondarily remodeled by processes 

 of precocious segregation"; and that the homologies which 

 are found between different embryos are none the less homolo- 

 gies because they are not bounded by definite cell walls ; nor 

 does the fact that in some cases cell walls do bound homologous 

 areas, have more than an accidental significance. 



