348 University of California Publications in Zoology. [Vol.4 



Fig. 1. — Lateral view of Pyropliacus horologicum with swarm spores. 

 X 300. After Schiitt ('96). 



Fig. 2. — Ventral view of the same after release of swarm spores by 

 opening the girdle suture. X 300. After Schiitt ('96). 



Fig. 3. — Diplopsalis lenticula after treatment with alkali, showing con- 

 tents escaping through the opened girdle suture. X 430. After Schiitt 

 ('95). 



Fig. 4. — Ventral view of Peridinium ovatum showing spreading of the 

 apical plates and the escape of the cell contents through the apical pore. 

 X 240. After Schiitt ('96). 



the other environmental conditions such as temperature are not 

 greatly modified. It seems probable that one or more of the 

 changed relations in matters of metabolism brought about by 

 these conditions may induce this total exuviation even in the nor- 

 mal habitat. 



2. Relation to schizogony.- — It is noteworthy that g'enera 

 which most perfectly exhibit simultaneous ecdysis without at- 

 tendant schizogony are, in the main, those which at fission and 

 spore formation abandon entirely the parental theca. This is 

 perhaps not a universal rule, for I have found in some species 



