6 BRITISH FRESHWATER RHIZOPODA. 



Tests with lobed apertures, such as those of Difflugia 

 corona, D. oviformis, and D. lobostoma, show a con- 

 siderable variation in the shape or number of the lobes, 

 but are nearly always symmetrical. 



Considering the manner in which Rhizopoda con- 

 struct their tests, the bi-lateral symmetry they nearly 

 always possess is very remarkable. Attention however 

 may be directed to one departure from this in the case 

 of curved tests, belonging to species which usually 

 possess them straight, found occasionally in very 

 restricted habitats ; one such, Diffluaia acuminata 



A' ' 



var. curvata Cash, is described in Volume I, and the 

 writer found in a pond in Long Island, U.S.A.,* two 

 species of Nebela and a Quadrulella thus modified, 

 and in Georgia, U.S.A., a curved species of Arcella 

 occurs. 



Reproduction in the Rhizopoda usually entails and 

 at certain stages may entirely consist of either multiple 

 or simple binary division. In the latter case the test, 

 if it is membranous or chitinous, may also divide, a 

 process which nearly always takes place in a longi- 

 tudinal direction; the more substantial tests, such as 

 those of the Difflugiae and Nebelae, do not divide. In 

 Volume III, Plate LIII, fig. 4, is an illustration of the 

 division of a test of Diaphoropodon mobile, and Plate 

 LVII, fig. 4, depicts what appears to be the commence- 

 ment of division in a transverse direction of a test of 

 Amphitrema flamim. 



In some genera or species the tests are protected by 

 a more or less thick covering of very fine hair-like cils 

 which appear to be secreted from the interior through 

 fine pores, as for instance Diaphoropodon mobile, Nebela 

 barbata, and species of Cochliopodium; and from Sierra 

 Leone a species of Difflugia has been recorded bearing 

 fine spines ; even one or tw T o amoeboid species are 

 thickly covered with very fine cils which disappear 

 and re-appear as the plasma flows, and must therefore 

 be protrusions of the plasma itself, e. g. Amoeba pilosa. 



* v. ' Journ. Linn. Soc., Zool.' vol. xxxii, pp. 136, 142. 



