PRIMORDIUM DEVELOPMENT 165 



First, multiplication of lateral striping is not essential for anlagen 

 formation, as shown when a large regenerator, for example, 

 induces the precipitous formation of a reorganization primordium 

 in a small, non-differentiating animal grafted to it. An anlage 

 appears which cuts across several stripes which show no splitting 

 whatever and an extensive presumptive frontal field is not pro- 

 duced (see Fig. 34B). Dissociability of stripe multiplication and 

 membranellar band formation is further indicated by the reciprocal 

 process of induced primordium resorption; for when this occurs 

 the new band disappears entirely but there is no regression of the 

 newly-multiplied fine stripes and ciliary rows which then contrast 

 sharply with the neighboring stripes remaining (Fig. 34A). 

 When a newly forming membranellar band is caused to be shed 

 by treatment with salt solutions at a relatively late stage in anlage 

 development, the multiplied fine striping can still be moved for- 

 ward to form a new frontal field, indicating that these stripes are 

 not merely shifted passively by the migrating adoral band (Fig. 41B). 



The disposition of the original anlage rift at stage i is not 

 rigidly fixed. It may run almost perpendicular to the striping or 

 its course may sometimes be considerably canted at about 30° to 

 the striping. In one case it slanted downward instead of upward 

 though this did not interfere with normal oral formation (Fig. 41 a). 

 The primordium opening need not cut across the lateral striping 

 at all. Thus Stevens (1903) observed that in longitudinal half 

 fragments the anlage appears in the line of heal which runs from 

 pole to pole. But this type of development is. shown most clearly 

 when the primordium, excised from a regenerating animal, is 

 replaced at once. The line of heal, at first tightly closed, opens to 

 permit the formation of a new primordium entirely parallel to 

 the striping (see Fig. 34B). Since such specimens were already in 

 regeneration, the new anlage develops very rapidly and there is 

 apparently insufficient time for stripe multiplication. After stage 6, 

 posterior ends of such replacing primordia curl to the right, 

 cutting through some of the relatively large preexisting stripes 

 which are carried forward to form new frontal fields of abnormal 

 appearance. 



The primordium need not develop as a unit or single entity 

 from the start. When through abortive fission a head-like struc- 

 ture remains athwart the primordium site, anlage development 



