Structure of Tests of Fresh-water Bhizopoda. 107 



which may perhaps extend over a period of some days. Previous 

 to division in many species an accumulation can be observed of 

 the necessary scales or disks, etc., required for the construction of 

 the daughter test, these being stored without any apparent order in 

 the body of the parent ; when grains of sand or other extraneous 

 materials are employed they are occasionally to be seen collected 

 around the aperture of the parent's test. 



The new test is commenced by building its aperture adjoining 

 that of the old test, and so course by course in rings until it is 

 completed. In cases where scales are employed, e.g. in the genus 

 Euglypha, the special aperture-scales are affixed first, and then the 

 body-scales and spine-scales or spines, until on its completion we 

 see two similar tests joined together by their apertures ; the 

 animal then divides, a moiety occupying each test, and on their 

 separating two mature and similar animals are the result. Care 

 must be taken not to mistake two animals conjugating for the 

 above, as the position of the two tests is similar. 



Ehizopoda tests can be grouped according to their structure in 

 four categories, viz., those composed of: 



1. A skin or shell more or less homogeneous. 



2. Extraneous materials collected by the animal. 



3. Extraneous materials modified by the animal. 



4. Materials, usually scales or disks of various forms, secreted 



by the animal itself. 



In the first group the tests may vary from a thin flexible 

 pellicle, which is a mere hardening of the ectoplasm, to a firm and 

 comparatively thick shell, such as those of the Arcellsz. 



Although hardly within this eatagory, the case of Amoeba pilosa 

 Cash (2) is well worth examination ; unfortunately this curious 

 species seems to be of rare occurrence. The plasma flows in the 

 usual amoeboid manner, but is covered with fine colourless hair-like 

 cils which appear on the lobular expansions as they are formed, 

 and are absorbed again when they are withdrawn. 



Cochliopodium bilimbosum (Auerbach) Leicly and other species 

 of that genus have flexible pellicles, colourless and transparent, 

 but in edge view, that is, in section, appear to be divided by trans- 

 verse strise at equal distances apart, whilst in face view a careful 

 examination reveals numerous punctuations, or rather minute beads 

 arranged in a series of lines radiating from the crown of the test. 

 Penard (4) thinks these markings may represent little pellets or 

 disks of a firmer substance than the rest of the test ; they are not 

 distinguishable in very young individuals. Careful treatment of 

 tests with a solvent of various degrees of strength might elucidate 

 the question. 



Species of the genus Gorycia have remarkably thin flexible 

 envelopes, the free edges of which, around the aperture, resemble 



i 2 



