Structure- of Tests of Fresh-ivater Rhizopoda. 1 1 5 



(PI. II, fig. 16) may be taken as typical of the first group. The 

 small disks of which the test is formed are from 1 • 5 /jl to 2 ■ 5 //, in 

 diameter and 1 • 5 fi to 2 yu, in thickness. They are affixed to a very 

 fine pellicle which lines the interior of the test, and are arranged 

 in several different ways (PI. Ill, figs. 27-29) ; they may lie closely 

 together in alternating or in parallel rows, or they may be separated 

 from each other by a distance equal to about one-third of their 

 diameter, in which case bands of darker-coloured cementing 

 material may usually be discerned joining each disk to its neigh- 

 bours (PI. Ill, fig. 30). In the majority of tests all the disks are 

 circular, but they may also be all oval, or circular and oval disks 

 may be mixed. 



Whether these differences in the structure of the tests are 

 inherited or merely individual variations is not known, but more 

 than two different variations of the test are seldom found in the 

 same gathering, and very often the tests from one locality are all 

 similar. 



0. ampulla var. major Penard (4) 1S distinguished from the 

 type by the presence of six (sometimes twelve) small pores around 

 each disk of the test (PL III, fig. 33). These pores are about ■ 5 jjl 

 in diameter and usually circular ; they are filled by a chitinous 

 material more soluble in acid than the rest of the test. 



Cyphoderia trochus Penard (4) an(1 its varieties (8) are charac- 

 terized by their tests being formed of small circular disks which 

 are convex on both sides and overlap each other ; they are arranged 

 in parallel rows ; the amount of imbrication varies in different 

 individuals, and even in different parts of the same test, being 

 greatest where the diameter of the test is least. The disks are 

 4c jx to 5 fM in diameter, and distinguishable under a moderate 

 magnification. These tests are easily examined if a portion be 

 broken off and mounted in a fairly liquid balsam, so that it can be 

 flattened out by pressure on the cover-glass ; an oil-immersion 

 objective can then be used with advantage. 



The various tests to which attention has been drawn in these 

 notes represent only a few of the species of fresh-water Ehizopoda, 

 many of which can be collected during a country walk or holiday 

 excursion. The beauty of the designs and the perfection of work- 

 manship expended on these little homes, together with their 

 permanence when mounted, should render them favourite objects 

 with microscopists, whilst for those who possess the requisite time 

 and patience to keep the living animals under observation there is 

 the incentive that at present their habits and modes of life offer an 

 almost unworked field of study, and the naturalist interested in the 

 problems of instinct, reason, and heredity is sure to gain, from 

 the study of these minute and primitive members of the animal 

 kingdom, information tending towards their solution. 



