DIFFERENTIAL DEVELOPMENTAL MODIFICATION. I 179 



on one side may determine slightly slower growth on that side because 

 parenchyma cells are less numerous. Figure 64, B, shows that the median 

 ganglionic region is apparently absent and that the more lateral parts of 

 the ganglia are approximated to the median line and partially fused. 



The teratomorphic head: This head is rounded anteriorly with median 

 eye, apparently single (cyclopia),^ and with cephalic lobes localized more 

 or less anteriorly instead of laterally and showing all degrees of approxi- 

 mation to the median line, with a single median lobe as the extreme (Fig. 

 63, D-G). The ganglionic modifications correspond in degree to those of 

 other parts of the head (Fig. 64, C, D). In the extreme teratomorphic 



Fig. 64, A-D. — Transverse sections of normal and differentially inhibited heads. A, 

 normal head of large animal; B, teratophthalmic; C, D, teratomorphic, reconstituted heads 

 (from Child and McKie, 191 1). 



forms (Fig. 63, G) the region corresponding to the normal head is only a 

 narrow median band, the median parts of the normal head not being 

 represented at all; the originally lateral regions of the normal head are 

 now anterior and near, or in the median plane. 



The anophthalmic form: In these forms the anterior regenerate may 

 resemble the extreme teratomorphic head with a single median cephalic 

 lobe but is without an eye (Fig. 6^, H), or the head may be represented 

 only by an outgrowth of new tissue without distinguishable external dif- 

 ferentiation (Fig. 63, /, /). The ganglionic mass shows various degrees 

 of more extreme reduction than in the teratomorphic head, and in some 

 cases only traces of gangHa appear at best; and it might even be ques- 



^ In sections two pigment cups forming a rounded mass and two nerves, side by side or 

 practically unite'd, or two pigment cups, one ventral to the other, are sometimes distinguish- 

 able; but usually there is only one (see Fig. 64, C, D). 



