Structure . of Tests of Fresh-iaater Bhizopoda. 113 



in section, tapering to a sharp point, and affixed to the scales where 

 they overlap. As the scales are arranged in longitudinal rows, it 

 follows that there is always an equal number of scales in any 

 transverse section of the test, and, therefore, the scales in the 

 broadest part of the test are the widest, and those at the crown the 

 narrowest ; they are all of the same length. If there are eight 

 aperture-scales there will be sixteen rows of scales, with, say, ten 

 scales in each row, making some 160 in all, a few being usually 

 omitted at the apex, and alb or nearly all, of these are formed by 

 the parent preparatory to building the test, and are stored with no 

 apparent order within its plasma. The question naturally arises 

 how it is able to sort out and affix each of these in its appropriate 

 position ; even if the body-scales are made narrow and widened 

 to suit the position in each case, the aperture-scales must be 

 selected, for they are often distinguishable among those stored up 

 ready for use, together with the spines which are subsequently 

 placed in position on the outside of the test. The process of 

 building such a test has never been observed in its entirety, but it 

 is to be hoped that the good fortune of some observer endowed 

 with the necessary time and patience will soon enable it to be 

 fully described. 



As a rule the body-scales of Euglypha tests are all very similar, 

 being elliptical or circular in form, but four species have scales 

 which are quite characteristic in each case ; the test of E. scutigera 

 Penard (8) has heart-shaped, or rather shield-shaped scales (PI. II. 

 fig. 9) ; those of E. crenulata Wailes (.9) are similar, but the base 

 or point of the shield is truncate and waved with three projection s 

 (PI. Ill, fig. 10), and those of its var. minor Wailes (9) are slightly 

 different in form with only one projection at the base (PL III, 

 fig. 11), whilst the scales of E. aspera Penard have projecting 

 thorn -like points on the upper part of each. 



On the other hand, the scales which border the apertures of 

 the tests are characteristic in every species, the variations consist- 

 ing in the number and shape of the teeth or points indenting their 

 free edges, also in their differences of size, thickness, and curva- 

 ture, thus rendering it possible to assign even an isolated aperture- 

 scale to the species to which it belongs. In examining these 

 scales on a test, care must be taken that their true shape is seen, 

 which owing to their curvature cannot be done when the test is 

 lying in a normal position, but the aperture has to be raised up 

 until the points of the scales lie in the plane of vision ; in the case 

 of small tests a considerable magnification and careful lighting arc 

 needed. 



The spines with which many species of Euglypha arm their 

 tests show considerable variety, both in shape and method of 

 attachment. They tall into two groups: (1) those which are 



