156 Dr. M. Verworn's Biological Studies of Protista. 



endeavour was to observe it in a form wliicli employs foreign 

 bodies in the construction of its sliell. For this I selected a 

 Difflugia. By the observations that I made upon this form I 

 was then induced to include a marine Poljthalamous form 

 {Volystomella) in the range of my studies, and I am indebted 

 to the kindness of Prof. F. E. Schulze for having the neces- 

 sary material placed at my disposal. 



Difflugia ueceolata, Carter. 



In an aquarium with water from the Halensee, near Ber- 

 lin, which had stood in the Berlin Zoological Institute since 

 the end of June 1887, numerous individuals of Difflugia 

 urccolata^ Carter, made their appearance towards the end of 

 October, and these, from their large size, furnished me with 

 favourable material for my investigations. In order to guard 

 against any sudden extermination of this brood of Protista in 

 consequence of unfavourable influences in the aquarium, I 

 separated from it several smaller cultures by distributing 

 many examples with portions of the bottom and aquatic plants 

 in small glasses which I kept in moist chambers. On exam- 

 ining one of these small glasses in the morning of November 

 9, I found two individuals engaged in conjugation. Any 

 mistake as to a process of division was here excluded, as the 

 shells of both individuals from the commencement of the 

 observation wei-e perfectly black, and by transmitted light 

 both appeared uniformly reddish brown. The two Protista 

 lay with their shell-openings so brought together that their 

 margins were exactly opposite each other, only upon one side 

 there was a narrow fissure between them, from which nume- 

 rous pseudopodia were protruded. The pair were isolated 

 and kept in a watch-glass. On the morning of the 10th 

 November all the pseudopodia were retracted, and the shells 

 lay immovably with the two openings pressed exactly 

 together. The Protista remained in this state throughout 

 the day. On November 11, in the morning, a small fissure 

 had again been produced between the mouths of the two 

 shells, and through this, as on the first day of observation, 

 numerous pseudopodia issued. As I assumed that the con- 

 jugation-process would soon be completed I killed the Pro- 

 tista with osmic acid in the course of tlie day, when the 

 pseudopodia remained exserted, and stained them with 

 ammonio-picrocarmine. It now appeared that during the 

 staining the two shells had separated from each other, by 

 which a glance into the nature of the protoplasm was rendered 



