6 14 PATTERNS AND PROBLEMS OF DEVELOPMENT 



pole of attachment of the larva, indicated by stippling in Figure 194, C, 

 was originally determined in the apical region of the early bud, a bending 

 or folding-over of the growing bud toward the center of the parental disk 

 would result in the position and form of Figure 194, C. Larval form and 

 invagination of the ciHated band suggest that such a bending or folding 

 by differential growth of the two sides may have taken place. The "cyto- 

 stome," which apparently has no function and disappears later, may also 

 result from a bending or folding of the larval body in early stages. Accord- 

 ing to this suggestion, the original polar axis of the larva is primarily 



A B 



Fig. 195, A, B. — Ophryodendron reversum; early stages of vermiform individuals developing 

 from buds; in B, dividing meganucleus (after Collin, 191 2). 



parallel to, and presumably determined by, either the parent axis or a 

 local bud activation and becomes bent so that the disk of attachment is 

 physiologically ventral, perhaps in consequence of a central-peripheral 

 radial differential in the parental distal region. The peripheral position 

 of the buds suggests that such a differential is present. In short, even the 

 larval pattern in these species may perhaps be determined by the relation 

 of the bud to the parent body. 



Certain suctorial species give rise, by external budding, to extremely 

 elongated vermiform individuals (Fig. 195) with longitudinal axes parallel 

 to the parental axis and apparently determined by it or resulting from a 

 local activation. Species of the genus Hypocoma, ectoparasitic on other 

 protozoa, and some other forms develop only a single suctorial tentacle 



