INTRODUCTION. 19 
and experiments to a typical Difflugia, D. wiceolato, 
conjointly with the marine Polystomella, 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 
Difflugia, 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 surface.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 
Diatomacee, 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 Huglypha, 
Quadrula, and other Monothalamia.” 
In order to verify these conclusions, Verworn, 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 Difflngix, but 
it was disregarded by the animals until a clumsy, 
entomostracan (Cypris) came near a Diffugiu, 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. fiir Wiss. Zool.,” xlvi, p. 455. (Transl. in ‘Ann. and Mag. 
Nat. Hist.,’ 1888). 
+ Bronn’s ‘ Klassen und Ord. des Thierreichs’ (1880). 
