ORDER II FORAMINIFERA 21 



with a large series showing difterent stages in development another phase of 

 the matter is presented. In certain cases there is a very decided change 

 in the condition of the aperture, but these changes appear at different stages 

 in the life-history, and all may be seen by cutting back a single full-grown 

 individual. In general, it has seemed from recent studies that apertural 

 characters, when studied in large series, are a rather dependable set for 

 systematic work, and this is true in the Miliolidae and Lagenidae especially. 



In many species teeth of various sorts are developed in the aperture, and 

 these teeth are subject to various modifications. It can be demonstrated 

 that these modifications occur in a definite sequence, and that this sequence is 

 important from a phylogenetic point of view. 



In a considerable number of genera a definite tubular neck is developed, 

 with the aperture at its end. This neck is seen in many genera 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 weak- 

 ness to the test, especially when it is at the edge of a thin chamber. Usually 

 in such cases, as in Orhitolites, 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. 



Many of the tests of the Foraminifera are beautifull}'' ornamented. Eaised 

 costae, striations, knobs, spines and punctate areas form the main types of orna- 

 mentation. Several of these or combinations of them may occur in a single 

 sjjecies, 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 chambers 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 specialised genera it is not uncommon to find certain 

 of the species with the early portion of the test ornamented, 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 

 BuUmina. 



Ordinarily the diff'erent 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. 



For many of the Foraminifera two distinct phases have been discovered. 

 One of these, the microspheric form, has a proloculum or first chamber of 

 much smaller size than the other — the megalospheric form. These two forms 

 are to be looked for in all species. 



The microspheric form (Fig. 4, B) has a number of nuclei, often a larger 

 number than there are chambers, scattered irregularly through the protoplasm 

 of the body. There seems to be a rather definite relation between the size of 

 the nuclei and the size of the chamber in which they occur, the larger nuclei 

 being in the larger chambers and the reverse. Apparently these nuclei simply 

 divide in their i-eproduction during the growth of the test. 



