254 The Sarcodina 



"excretory granules." It has been suggested that these inclusions are 

 accumulated pigments derived from diatoms or other food. 



Tests. On the basis of their construction, two varieties of tests may be 

 recognized — tests composed entirely of secreted materials; and arenaceous 

 tests consisting mainly of foreign materials held together by a secreted 

 cement. Throughout the order there appears a primitive "chitinous" test 

 which may become the definitive test of the adult, as in Allogromiidae 

 (Fig. 5. 43, 44) and such types as Iridia lucida (81). It is uncertain 

 whether this test is secreted by the myxopodia or is produced by actual 

 transformation of an outer pseudopodial reticulum. In most species, the 

 initial chitinous test is strengthened by the addition of inorganic salts or 

 of foreign particles during development of the organism. In any case, the 

 test is enclosed in a layer of cytoplasm continuous with the pseudopodia. 



The basic structure of the arenaceous test is a thin "chitinous" layer. 

 Onto this layer are cemented sand grains, sponge spicules, ambulacral 

 plates of echinoderms, fragments of other tests, and the like (Fig. 5. 36, 

 A-D). Such particles are picked up by the pseudopodia and pulled to the 

 initial chitinous layer, where they are cemented into a wall. The more 

 primitive species show no discrimination. Others tend to use a particular 

 type of structural element, so that different species collected from the 

 same area may show characteristic differences in construction of their 

 tests. The nature of the cement varies with the species. In some of the 

 primitive forms, the cement is chitinous, like the initial layer of the test. 

 The most common is an orange to brownish material, supposedly con- 

 taining iron and often known as "ferruginous" cement. A number of 

 species produce a calcareous cement, and there are also a few in which 

 the cement is siliceous. Arenaceous tests are found in about a third of the 

 established families. 



Calcareous tests, the predominant modern type, and the relatively rare 

 siliceous tests differ from arenaceous tests in the absence of foreign par- 

 ticles. There are, however, interesting cases in which the first few cham- 

 bers produced by the young organism are arenaceous while the later ones 

 are strictly calcareous. Such ontogenetic evidence, and the existence of 

 species forming graded series from typically arenaceous to completely 

 calcareous tests, support the assumption (30) that the cement of primitive 

 tests gradually became the predominant building material during evolu- 

 tion of the group. 



Growth of the individual, in primitive types, may involve desertion of 

 the old test and the construction of a new and larger one (30). The more 

 specialized types merely add new chambers to the preceding ones as 

 growth continues (Fig. 5. 35, A-C). In different species, the new chambers 

 are added in characteristic series, and within reasonable limits, in rela- 

 tively characteristic numbers to produce the test of the adult. The result 

 is a wide variety of patterns (Fig. 5. 37). 



