6o8 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



tation of a part of the cytoplasm about certain "generative" nuclei, which 

 are thus distinguishable from other "somatic" nuclei. An example of myx- 

 osporidian spore development is given in Figure 191, with A showing the 

 two spores of a pansporoblast in a developmental stage, B a single spore of 

 somewhat later stage, and C the elongated form of the mature spore. This 

 spore is essentially a multicellular axiate organism, and its development 

 presents various problems. What determines the difference between gen- 

 erative and somatic nuclei in the multinucleate amoeboid mass, resulting 



B C 



Fig. 191, A, B. — Stages of spore development of a myxosporidian, Ceratomyxa drepaiwp- 

 settae. A , the two spores in amoeboid body, partially developed envelope, polar capsule cells 

 and polar capsules outlined; spiral thread present at this stage, but not shown in figure; bi- 

 nucleate germ stippled. B, later stage of a spore, spiral threads of polar capsules indicated in 

 section. C, form of mature spore (after Awerinzew, 1909). 



in formation of delimited cell bodies about the former and not about the 

 latter? What determines the axiate pattern and the differences in be- 

 havior of cells, resulting in development of polar capsules, envelope, and 

 binucleate germ in a definite spatial pattern? These differences in fate 

 apparently involve differentiation of capsule cells and envelope cells along 

 quite different lines. The orientation of the two spores in Figure 191, A, 

 suggests axial determination in reaction to some factor external to the 

 pansporoblast, but various figures of this and other species show no indi- 

 cation of a general factor that might determine such pattern. As regards 

 certain features of cnidosporidian development, there is difference of 

 opinion among investigators; but there is no question concerning develop- 



