ORIGINS OF AGAMIC PATTERNS 609 



ment of a multicellular axiate pattern in both myxosporidian and actino- 

 sporidian spores. 



The extremely minute spores of the order Microsporidia possess a single 

 polar capsule or vacuole with long thread. Certain data suggest that in 

 some species the axiate spore pattern may be determined by factors in 

 the host cells, perhaps the physiological polarity of these cells, within 

 which the spores are formed. In the genus Ciirleya, however, the panspo- 

 roblast, containing four nuclei, gives rise to four spores by elongation in 

 four directions, the like poles of each of the four spores being, respectively, 

 peripheral and central as regards the whole group, as if determined by the 

 differential between surface and interior of the group. 



As regards many species, there is no evidence that the "germ" of the 

 spore possesses or retains any trace of axiate pattern in the later amoeboid 

 stage. Some of the Myxosporidia are apparently axiate in the amoeboid 

 stage, but whether this pattern is determined in the spore is not known. 

 The small size and parasitic habit of these forms present difficulties to 

 experimental control, but the many problems concerning developmental 

 patterns in the group are no less important than those of embryonic de- 

 velopment.^ 



PATTERNS OF "eMBRYONIC" OR "lARVAl" STAGES OF SUCTORIA 



The Suctoria show various types of budding, and the life-cycle involves 

 metamorphosis of a ciliated, free-swimming stage into a suctorial form, 

 usually sessile. Some particularly interesting and puzzling questions con- 

 cerning pattern arise in connection with origin and development of the 

 buds.-* The ciliated stages, sometimes called "embryos" — perhaps prefer- 

 ably "larvae" — show in different species considerable differences in axiate 

 and ciliary patterns and in manner of origin from the parent body. As 

 will appear, designation of the axes is, to some extent, a matter of view- 

 point. The disk of attachment of the later suctorial stage is usually visible 

 in the free-swimming larval forms; and since this constitutes one end of 

 the chief — often the only — axis of the suctorial form, it seems most con- 

 venient, though not necessarily otherwise significant, to regard it as rep- 

 resenting one end of the polar or chief axis in the ciliated stage. Collin, 

 however, regards this axis as dorsiventral. 



3 It has been possible to mention only a few of the interesting features of this material. 

 Further data appear in Doflein-Reichenow, 1929, and in the literature cited there. 



* The types of budding and forms of the ciliated stages are described at length in the mono- 

 graph by Collin (191 1, 1912), which has an extensive bibliography. 



