J42 



Äctiuosj>haenuin Eivhonü 



two polar bodies ; the daughter cysts then fuse, about twenty-four hours after their 

 formation, sister with sister, to form circular discoid coujugatioa cysts each con- 

 taining a conjugation iiudeiis. The conjugation cysts form thick siliceous coats 

 and remain in this condition for several weeks. 



Preliminarji Experiments and Ohservations. 



The free living Actvnosphaeria possess a great many iiiore nuclei than the few 

 that are preserved for this process of enc^'stment : iny first object therefore was to 

 deterniiiie roughly how many nuclei are thrown away in the process of encyst- 

 ment. For this purpose I took several hnndrcd iiulividuals of varioiis sizes, 

 measured them*, put three-qnarters to starve and in consequence to encyst (at 

 rooni tomperatnrc l.r — 19° C), and killed and stained the romaining quarter in 

 Order to couut their nuclei. The results of these two experinieuts are set forth in 

 Tables I. and II. 



ü 



o 



05 



3 





s 



s 



TABLE I. 



Diameter of Individuals in Micrometer Units. 



* Every precaution was taken to ensure accuracy in tho measurement. Each specimcn was 

 measured with a micromcter under Zeiss AA, 2, the unit of meaBiiremcnt being one division of an 

 eye-piece micrometer, which was found with the objectivo uscd to correspond to 1-81 ft. The creatures 

 were selected (or measurement only whcn the pseudopodia wcre fuUy expanded, the contour of the body 

 was circular, and the creature was suspended freely in a drop of watcr. The dianietcr of tho body was 

 then taken frora edge to cdge, ignoring the pseudopodia. The difliculty of deterniining the correlation 

 between the size of Actinosphaeria and the number of cysts built was encouutered chiefly in the 

 liability of the creatures to divide or fuse one witli another (plastogamy) after they had been placed in 

 the vessels to starve and to encyst. To avoid mistakcs from this cause the vessels were kept as constnntly 

 under supervision as possible, and discretion has been used in various ways : but absolute accuracy in 

 cases of such difliculty can hardly be ensured. 



