74 



to ambient temperatures as are most poikilotherms . Thus, 

 the stability of quaternary enz3niie structure may be more 

 critical in this microsporidi\am. 



We may only speculate as to the physiological function(s) 

 that may be inhibited by extremes of temperature. However, 

 the critical event in MB sporulation may well be meiosis. 

 If the sister nuclei of the diplocaryon found in NMB spores 

 and the vegetative stages of B. dimorpha are each diploid, 

 meiosis would produce eight uninucleate (haploid) spores 

 (MB spores occur in octets bound by a membrane) . Evidence 

 that meiosis does indeed occur in microsporidia has been 

 published by Loubes et al. (1976) and Hazard et al. (1979). 



The hypothesis that meiosis may be the critical event 

 in MB sporulation inhibition by extremes of temperature 

 is at least circumstantially supported by the essentially 

 complete absence of MB spores in specimens placed at 20 

 or 32° C at an age before eye development becomes visible, 

 and the partial and highly variable degree of inhibition 

 in specimens exhibiting early eye development. The appear- 

 ance of MB sporoblasts approximately coincides with the 

 earliest visible eye development. At this stage, second 

 cycle meronts enlarge to the full size of mature pansporo- 

 blasts, and the diplocaryotic nuclei become very diffuse. 

 Successive nuclear divisions then produce plasmodia containing 

 two, four, and finally eight nuclei. Endogenous cytoplasmic 

 budding around these nuclei produces an octet of uninucleate 



