THE TEST 11 



in a few groups, notably the Silicinidae although siliceous 

 tests may be developed in the Miliolidae as will be noted later. 

 Calcareous cement is used in some shallow water tropical forms'. 



Siliceous Tests. In a very few groups siliceous tests may be 

 developed. In the Silicinidae such tests are the rule. In the 

 more primitive Miliolidae under brackish water or deep sea con- 

 ditions tests of nearly pure silica may be developed. This is an 

 unusual form of test for the foraminifera. 



Calcareous Tests. In the Miliolidae and Ophthalmidiidae 

 there are developed entirely imperforate tests of calcareous 

 material. In the more primitive Miliolidae there may be sand 

 grains incorporated in the exterior but only as a secondary fea- 

 ture. In the Peneroplidae and related families an imperforate 

 test is developed after a perforate young showing that in these 

 families the imperforate character is a secondary and not a 

 primitive one. 



In the majority of species of the foraminifera, perforate cal- 

 careous tests are the rule. These may be thin and nearly trans- 

 parent as in m.any species of Lagena or of very heavy character 

 and large size as in the orbitoids. The perforations may be very 

 small and fine or very large and coarse, with sometimes more 

 than one kind in a single test, Orbulina, etc. In some tests the 

 early stages may be very finely perforated and in successive 

 chambers increase in size until the adult chambers are very 

 coarsely perforate, and the reverse may be true in other species. 



Forms of the Test. The simplest form of test is that of the 

 Astrorhizidae where there is a central body and numerous chan- 

 nels out to the surface, representing the material collected about 

 the pseudopodia. In the Rhizamminidae there are two open 

 ends. In the Saccamminidae, the chamber becomes more defin- 

 ite, and a single aperture is developed. After the single cham- 

 ber, the next stage in development is the formation of an elon- 

 gate tubular chamber usually coiled about the proloculum or 

 first chamber. This may then be broken up into irregular cham- 

 bers and finally into the definitely chambered forms. Uncoiling 

 as elsewhere in the animal kingdom is often a sign of gerontic or 

 old age characters. In the foraminifera as in other groups this 

 may finally result in specialized, almost or wholly uncoiled, 

 forms. The primitive coiled forms may be planispiral or may 

 develop conical or even cylindrical spirals. From the planispiral 



