6 BULLETIN 71, UNITED STATES NATIONAL MUSEUM. 



in a great many modifications, and in Lagena the tube may be inverted 

 and be directed into the chamber of the test. 



It is obvious that a very long slit-like aperture may be a source of 

 weakness to the test, especially when it is at the edge of a thin cham- 

 ber. Usually in such cases, as in Orbitolites, the animal changes its 

 aperture from a single one in each chamber to a considerable number. 

 This is often coincident with the development of chamberlets, but not 

 invariably so, for multiple apertures occur in Peneroplis where there 

 are no chamberlets. 



ORNAMENTATION. 



Many of the tests of the Foraminifera are beautifully ornamented. 

 Raised costse, striations, knobs, spines, and punctate areas form the 

 main types of ornamentation. Several of these or combinations of 

 them may occur in a single species, the form of the ornamentation 

 often changing as the chambers of the test are developed. Certain 

 of the simpler forms of ornamentation may occur as parallelisms in 

 widely separated groups. As a rule, the proloculum and early cham- 

 bers are smooth and unornamented, but there are certain exceptions, 

 as in Nodosaria, for example, where in some species ornamentation may 

 occur on the first chamber. In specialized genera it is not uncommon 

 to find certain of the species with the early portion of the test orna- 

 mented, but the last-formed chambers with a loss of ornamentation 

 and a consequent development of smooth chambers. On the other 

 hand, there may be a thickening of the test from without and the 

 covering of the chambers already formed with a secondary growth, 

 often spinose. Such a condition is seen in some species of Bulimina. 



SECONDARY CANAL SYSTEMS. 



Ordinarily the different parts of the test are connected with one 

 another by the previous apertures, but in some cases, notably in 

 Polystomella, there is a secondary canal system which is very complex 

 and runs to all the parts. This has been worked out by Carpenter 

 and others in detail. 



The color of the empty tests in the Foraminifera is not a prominent 

 feature. Among the arenaceous forms the cement is often ferruginous, 

 and when the iron is in sufficiently large proportion it imparts a red- 

 dish or yellowish-brown tinge to the whole structure. With this ex- 

 ception the arenaceous forms are usually dependent for their coloring 

 upon the material from which the test is made up. This material 

 may be of various colors, from the white of coral or siliceous sands to 

 black, with the various colors usually associated with ordinary sand 

 particles. In living specimens of certain of the arenaceous types, 

 Ammodiscus for example, the newly formed portion of the test is 



