4 BULLETIN 71, UNITED STATES NATIONAL MUSEUM. 



are derived from the perforate group and that the lack of pores instead 

 of being a primitive condition may in reality be a specialized one 

 derived from a condition in which pores were developed throughout 

 the life of the individual. 



In general the test of the Foraminifera may be single chambered or 

 many chambered. Contrary to the impression given by certain 

 works on the group, the process of adding chambers in the Foram- 

 inifera, while superficially like budding or gemmation, is not neces- 

 sarily or usually accompanied by nuclear divisions. That is, instead 

 of the new chambers being potential individuals they are simply inte- 

 gral parts of one cell, and in the uninucleate form the single nucleus 

 is found in about numerically the middle chamber. In the process 

 of adding a new chamber a portion of the protoplasm is protruded 

 from the aperture and a new chamber wall then formed about it. 

 In some cases a complete wall is formed with each newly added cham- 

 ber, but in others the adjacent parts of previous chambers form the 

 inner walls of the new chamber and new walls are formed only on the 

 free parts of the protoplasmic mass. In the open tubular test, such 

 as Astrorhiza or Hyperammina, increase in the protoplasmic body is 

 accompanied by addition of material at the open end of the tube and 

 an increase in size results. In single-chambered types, such as 

 Lagena, the manner of increase in size is problematical, if there be any 

 at all. In such forms the entire test may be made in its completed 

 form at once after division, as is the case with certain of the fresh- 

 water Rhizopods. 



STRUCTURE. 



COMPLEX TESTS. 



In the tests having more than a single chamber the apertures of the 

 first-formed chambers become internal, as a rule, and a complexity 

 of relations to the outside medium is thus brought about. One of 

 the simplest arrangements of the chambers is a linear series. Such 

 an arrangement is seen in Reophax and Hormosina. Another very 

 common plan of arrangement is a planospiral, as in Ammodiscus. 

 This may be varied by having the revolving line in a spire and then 

 the whole test becomes trochoid, as in Trocliammina. Another common 

 arrangement is a biserial one, the chambers being on opposite sides 

 of the axis, as in Textularia. These four plans or some modification of 

 them are the characteristic arrangements for the chambers in most 

 of the secreted tests. Oftentimes more than one plan of arrangement 

 enters into the formation of the test. Dimorphism was used for this, 

 but that term has been used elsewhere with a very different meaning. 

 As here viewed, this life history with several distinct methods of 

 growth has a deeper significance than has usually been attached to it. 

 It seems to have a definite phylogenetic bearing in each particular 



