INTRODUCTION. 17 
chitinous envelope, fortify and ornament it externally 
with sand-grains, diatom-tests, and other extraneous 
substances. 
The tests of Hyalosphenia are either plane-surfaced, 
or ornamented with variously-disposed pits or depres- 
sions. Those of Nebela and Huglypha are built up of 
circular, oval, or hexagonal plates, placed edge to 
edge, or with the edges overlapping. 
The development of the Rhizopodous tests has been 
closely studied by Gruber, Verworn, and others. In 
Fic. 7.—Test of Hyalosphenia papilio. x about 250. Fie. 8.—Test 
of Diflugia pyriformis (a common form) encrusted with sand- 
grains. x 200. 
Buglypha alveolata Gruber concluded that there was a 
development, within the protoplasmic body, of the 
necessary materials—chitin, cellulose, or silica—by 
chemical agency. Diaphanous plates of varied pattern, 
circular or oval (Nebela, etc.). polygonal (some 
Euglyphz); quadrangular (Quadrula); or of no definite 
geometrical figure, are secreted; and during mitosis 
(reproductive fission) these so arrange themselves in 
the newly-formed cell as ultimately to form an external 
covering, in all respects like that of the parent.* It is 
* © Zeitschr. fir Wiss. Zool.,’ xxxv (1881), 431. See also Schewiakoff in 
‘Morphol. Jahrb.,’ xiii (1888). 9 
