536 CHARLES W. HARGITT 
this connection. With certain limited aspects of the problem 
as they relate to coelenterate ontogeny facts have come to knowl- 
edge which demand consideration. In a general way it may be 
said of the problem of cleavage homology that two rather diverg- 
ent schools of biologic thought have grown up. One of these, 
ably represented by Driesch and O. Hertwig, maintain that cleayv- 
age is a more or less general and quantitive process, the result- 
ing blastomeres being largely equipotent in later development, 
their individual values depending largely upon relations of posi- 
tion, ete. The other wing of thought would hold that cleavage 
is fundamentally a qualitative process, involving a nicely pre- 
determined and ‘orderly sifting of materials,’ resulting in a splen- 
did ‘mosaic work,’ each cell fitted into its predetermined place 
with mathematical precision. Under the latter conception 
‘cell lineage’ became the dominant problem of embryological 
research. 
As a corollary to this, not only were blastomeres factors of 
supreme concern, but the natural and almost necessary implica- 
tion followed that there must of necessity be predetermining 
factors in the unsegmented egg even more fundamental than those 
in the blastomeres. Hence came into prominence the search for 
evidences of ‘formative stuffs’, ‘prelocalized germinal areas’, 
etc. Watving all further consideration of this particular aspect 
of the problem in its theoretical implications, I may very briefly 
cite facts concerned. with coelenterate cytology, and attempt to 
show their bearing in the case. 
In earlier contributions on the subject.of cleavage, partic- 
ularly in Pennaria and Clava, and further facts given in previous 
parts of the present paper, attention has been directed to facts 
which must be their own exponents. As to any blastomere homo- 
logy in any of these cases it is difficult to conceive. Further- 
more, both under normal conditions and through experiment, it 
has been demonstrated over and over that one or many blasto- 
meres may be detached without in the least modifying the course 
of development in any particular. With such pictures as those 
in figures 1 to 30 before one, he would need be possessed of a measure 
of imagination beyond compare who could discern any sign of a 
