456 



BIOLOGY OF THE PROTOZOA 



in some cases without any. The capsules and threads are invisible 

 or very difficult to see in the living spore (hence crv'ptocysts) , but 

 are demonstrable upon treatment with alkalies. The spore capsule 

 is bivalved in some but consists of a single piece in other species. 

 The history of spore-formation agrees in the main with that of the 



Fig. 190. — Stempellia magna, life cycle. A, Developmental stages of young 

 amcebula from spore S.; B, stage of nuclear increase; C, formation of sporont; D, 

 formation of a single spore, -E, formation of two spores; F, formation of four spores; 

 G, of eight spores; H, development of iminucleated spore with polar capsule. (After 

 Kudo.) 



Myxosporidia but authorities disagree as to details and convincing 

 proof is yet to be demonstrated. Fertilization processes have been 

 described by Mercier (1908, 1909) whereby two isogametes of Thelo- 

 hania giardi fuse to form the pansporoblast, an observation which 

 has not been confirmed. Autogamous union of nuclei prior to 

 spore-formation and not, as in Myxosporidia in the later sporo- 



