RHIZOPODA 



55 



nous. Ai^-ain, the shell may be encrusted with sand-grains derived 

 directly from without, or from ingested particles, as shown in 

 Caitropyxis, Diffiugia (Fig. 10, D), Hehoiiera, and Campascus 

 when supplied with powdered glass instead of sand. The 

 cement in Difflugia is a sort of organic mortar, infiltrated 

 with ferric oxide (more probably ferric hydrate). In Lecqiieu- 

 reusia spiralis (formerly united with Difflugia) the test is formed 

 of minute sausage-shaped 

 granules, in which may be 

 identified the partly dis- 

 solved valves of Diatoms 

 taken as food ; it is spir- 

 ally twisted at the apex, 

 as if it had enlarged after 

 its first formation, a very 

 rare occurrence in this 

 group. The most frequent 

 mode of fission in the tes- 

 taceous Ehizopods (Figs. 

 8, 10) is what Schaudinn 

 aptly terms "bud-fission," 

 where half the protoplasm 

 protrudes and accumu- 

 lates at the mouth of the 

 shell, and remains till a 

 test has formed for it, 

 while the other half re- 

 tains the test of the 

 original animal. The 

 materials for the shell, 

 whether sand -granules or plates, pass from the depths of the 

 original shell outwards into the naked cell, and through its cyto- 

 plasm to the surface, where they become connected by cementing 

 matter into a continuous test. The nucleus now divides into two, 

 one of which passes into the external animal ; after this the two 

 daughter-cells separate, the one with the old shell, the other, 

 larger, with the new one. 



If two individuals of the shelled species undergo bud-fission 

 in close proximity, the offspring may partially coalesce, so that a 

 monstrous shell is produced having two pylomes. 



Fig. 10. — Test- 1 tearing Rhizopods. A, Qvadrnla 

 syvtmelrica ; B, Hyalosphenla lata ; C, Arcella 

 vulgaris ; D, Difflvgia pyriformis. (Fioni Lang's 

 Comparative Anatomy.) 



