INTRODUCTION. 19 



and experiments to a typical Diffiugia, I). urceohtt<i, 

 conjointly with the marine Poli/stomella, in order to 

 ascertain the relation of the plasma-body in each case 

 to the shell-structure and the behaviour of the animals 

 under artificial conditions. The body of an individual 

 DiffliKjift, a portion of whose shell had been removed, 

 was found to be charged with sand-grains, some lying 

 apparently only adherent to, but others completely 

 immersed in, the protoplasm.* Biitschli had some 

 years previously, says this author, intimated the pro- 

 bability that the foreign material employed in the 

 construction of the Difflugian shell was taken up into 

 the protoplasmic body of the animal itself, and subse- 

 quently deposited at the surf ace. t And Gruber, 

 adopting this suggestion, and with reference to the 

 frequently-observed phenomenon that other Rhizopods 

 take up sand-grains, said : " Scarcely any doubt will 

 remain that Biitschli's opinion with regard to the 

 Difflugian shell is correct, and consequently these 

 animals themselves will select and take up into them- 

 selves from the water the material the sand, the 

 Diatomaceae, or whatever it may be. They thus pro- 

 ceed to divide themselves, and the formation of the 

 new shell takes place in the same way as in Euglypha, 

 Quadruld; and other Monothalamia." 



In order to verify these conclusions, Vervvorn, in 

 the first place, ascertained the fact of the inception of 

 sand-grains. Finely-powdered dark blue glass was 

 introduced into the water with living Diffl,ugise t but 

 it was disregarded by the animals until a clumsy 

 entomostracan (Cypris) came near a Difflngia, and 

 pushed roughly against its pseudopodia. In a few 

 seconds the surface of the widely-extended pseudo- 

 podia became wrinkled and knobbed, and some particles 

 of ground glass were observed adhering to them. 

 They were gradually absorbed completely into the 

 interior of the shell along with the pseudopodia. It 



* ' Zeitschr. f iir Wiss. Zool./ xlvi, p. 455. (Transl. in ' Ann. and Mag. 

 Nat. Hist.,' 1888). 



t Bronn's ' Klassen und Ord. des Thierreichs' (1880). 



