(3) 



CONSTRUCTION OF THE TESTS OF THE CONCHULINA. 



Owing to the wide range of variation in the form 

 of tests which occurs in many species of testaceous 

 Rhizopoda, the determination of the limits of species 

 and varieties is a subject fraught with difficulty and one 

 upon which there are many diverse opinions. A brief 

 resume of the conditions, so far as we know them, 

 under which these tests are constructed, would seem 

 not out of place here and should be helpful in con- 

 sidering the problems so frequently presented to 

 observers of Rhizopod life. 



There are broadly two classes of tests, those secreted 

 by the animal itself and those which it builds up of 

 extraneous materials; the former are less subject to 

 variation than the latter, not of course taking into 

 account those variations of shape in flexible tests 

 which the animal can execute at will or which are due 

 to ingested food, and this greater conformity to type 

 is only what might be expected to occur in the case of 

 those tests which are formed of natural secretions and 

 are moulded on the animal's body. There are forms 

 of secreted tests in which whilst the elements of the 

 test are secreted naturally in the plasma, the test as 

 a whole is built up from these elements by the efforts 

 of the animal itself ; thus, in the genus Euylypha, when 

 a new daughter test is about to be produced, all the 

 necessary elements may be seen accumulated in readi- 

 ness in the plasma ; aperture-scales, body-scales, spine- 

 scales, or loose spines can all be distinguished among 

 the collection, but their sorting-out, building-up, and 

 cementing together are dependent upon the animal's 

 more or less voluntary efforts, and when the appa- 

 rently very inadequate equipment of the animal for 

 this purpose is considered, it is surprising that the 

 tests should exhibit so much uniformity. 



Of those Rhizopoda which form their tests from 



1* 



