838 THE ANIMAL KINGDOM. 



Orbitolites, Alveolina, perfect in the perforate Cycloclypeinae. In recent 

 species of Alveolina the chamberlets in turn are subdivided. The septa 

 dividing the chambers in the imperforate Foraminifera and the simpler 

 perforate, are single and formed by a portion of the outer wall of 

 the preceding chamber ; in the higher perforate forms, e. g. larger 

 species of Rotalia, in Polystomella, they are double, a second layer being 

 added to the surface of the old chamber at the formation of a new 

 chamber. The first, primordial, or embryonal chamber differs from its 

 successors ; it is globular, ovate or lens-like. The difference is naturally 

 most marked in complicated shells. In some Rotalidae and Nummu- 

 linidae there is a supplemental, exogenous, or secondary skeleton in 

 addition to the chamber walls proper. This secondary deposit may fill 

 up the depressions between successive chambers and the central umbilical 

 cavities due to the increasing size of successive coils, or it may coat the 

 entire test as in Calcarina and Heterostegina. Small projecting masses 

 of it are found between the edges of the chamberlets in the Cycloclypeinae. 

 It may grow out into spines between the chambers of the larger species 

 of Rotalia, or from the surface in" general as in Calcarina. A system of 

 more or less complicated ' interseptal ' canals opening superficially is 

 usually developed in connection with this skeleton between the convo- 

 lutions and septa : by its means the protoplasm of the more deeply 

 situated parts communicates with the surface. The surface of the test 

 may be ornamented with pits, areolae, ridges or bands ; it is sometimes 

 spinulose, in Globigermidae especially, the spines attaining a great length 

 and being moveable in Hastigerina. With few exceptions the test itself 

 is colourless ; it is red in Polytrema and Globigerina rubra. 



An adventitious skeleton is characteristic of the two families Astro- 

 rhizidae and Lituolidae. The material of which it is composed is selected 

 and is in most instances sand-grains, which are loose with very little 

 cement indeed in Astrorhizinae, in others generally cemented firmly 

 together. The nature of the cement varies ; it is chitinous, and the test 

 flexible in Rhizammina or brittle in Rheophax membranacea ; as a rule it 

 consists of Ferric oxide and Calcium carbonate in varying proportions, the 

 former being especially predominant in some Lituolidae, viz. 16-3 percent, in 

 Haplophragmium latidorsatum, and 9-4 per cent, in Cyclammina cancellata. It 

 is very rarely siliceous, e. g. in Rheophax nodulosa. The surface of the test is 

 generally rough, but in the Trochammininae it is smooth and polished, being 

 composed of a large amount of cement with very fine sand-grains. Mud 

 coating a chitinoid membrane is found in the Astrorhizine Pelosina ; so too 

 in Dendrophrya, but the chitinoid membrane is beset with sand-grains. 

 Sponge-spicules felted together, mixed with fine sand but not united by 

 cement, characterise the test of the Pilulininae. Sponge-spicules are 

 also preferentially selected by Haliphysema mixed with other foreign 



