ORIGINS OF AGAMIC PATTERNS 



613 



P. fixa, for example, develops from the apical region of the parent, the 

 cilia covering its whole body replacing the suctorial tentacles progres- 

 sively from the free end proximally (Fig. 194, A). Larval development 

 from an external bud in a manner like the development from internal 

 buds shown in Figure 193, A-D, has also been observed in some species 

 (Fig. 194, B) and again raises the question of relation of bud axis and 

 parental axis. According to Collin, the bud axis in these forms is usually 

 transverse to the parental axis but may be oblique, as in Figure 194, B. 

 This figure suggests, however, that the bud axis may have been primarily 

 parallel to the parental axis. 



Fig. 194, A-C. — Larval development from external buds in Suctoria. A, Podophrya; B, 

 Paracineta patula; C, Ephestia gemmipara in sagittal section, showing invaginated ciliary band 

 near free end, "cytostome" near attached end, and pole of attachment indicated by secretory 

 granules (after Collin, 19 12). 



Larvae of some other species develop from external buds arising in a 

 circle about the periphery of the more or less flattened distal or apical 

 surface of the suctorial form. In a typical case the surface of the bud 

 toward the center of the parental disk becomes flattened ; the disk of at- 

 tachment and rows of cilia develop on it, the ciliated region becoming 

 invaginated ; and an infolding, regarded by Collin as a rudimentary cyto- 

 stome, also appears near the attached end of the larva (Fig. 194, C). In 

 such larvae the polar axis, indicated by the disk of attachment, either has 

 become physiologically dorsiventral, and is transverse or oblique to the 

 suctorial parental axis, or is bent in a right angle. The larva shows an 

 anteroposterior pattern parallel to the parental axis. It is not evident 

 from the descriptions and figures how this pattern originates, but the 

 following suggestion may possibly have some value. Assuming that the 



