PROTOZOA. 29 



formed, Verworn 1 isolated a specimen and gave it splinters 

 of blue glass. He observed repeatedly that the Difflugia 

 crept by the splinters, its pseudopodia pushing them away 

 instead of taking them up. After a time a Cypris passed 

 and irritated the pseudopodia, which caused a sticky secre- 

 tion to form on their surface, so that pieces of glass were 

 caught in it and were then taken into the body with the 

 pseudopodia. 



Afterward Verworn irritated the pseudopodia with a 

 needle; the surface became rough and took up glass 

 which before it did not do. The splinters were really 

 drawn into the protoplasm so that the interior contained 

 a little heap of them. These observations tend to prove 

 that the origin of the shell of Difflugia urceolata is 

 mechanical and largely a matter of accident. 



Later experiments upon Difflugia lobostoma Verworn,' 2 

 tend to prove that the animal does not exhibit a conscious 

 choice in the taking up of material for its shell, nor does 

 there seem to be any calculation in regard to the quantity 

 of sand grains or glass splinters needed. Sometimes a 

 mass was taken and then thrown out in order apparently 

 to take up more a desire to get, it would seem, rather 

 than to use. 



Verworn saw two, three, and even five zoons of this 

 species of Difflugia in conjugation. He proved by experi- 

 ment that two zoons might touch each other for a long 

 time without blending, while other zoons united with the 

 fusion of the protoplasm. Experiments were made to 

 cause zoons to blend by keeping two close together, but 

 were unsuccessful, and the author considers that it is 

 proved indubitably that every zoon cannot blend with 

 every other. On the other hand, two zoons which were 

 in conjugation were separated but these came together 

 again, showing that one must exert a directive influence 

 upon the other or the two upon each other. The cause 

 may be of a chemical nature, as maintained by Verworn. 



1 Zeitschr. f. wiss. Zool., XLVI, 1888, Heft IV, p. 455. 



2 Zeitschr. f. wiss. Zool., L, Heft 3, 1890, p. 449. 



