346 PR()T0Z()0L0(;Y 



by asexual reproduction (Fig. 157). The former is ordinarily 

 small and known as the microspheric proloculum (a), while the 

 latter, which is usually large, is called the megalo spheric pro- 

 loculum (e). To the proloculum are added many chambers which 

 may be closely or loosely coiled or not coiled at all. These cham- 

 bers are ordinarily undivided, but in many higher forms they are 

 divided into chamberlets. The chambers are deHmited by the 

 suture on the exterior of the shell. The septa which divide the 

 chambers are perforated by one or more foramina known as 

 stolon canals, through which the protoplasm extends throughout 

 the chambers. The last chamber has one or more apertures of 

 variable sizes, through which the cytoplasm extends to the ex- 

 terior as pseudopodia. The food of Foraminifera consists mostly 

 of diatoms and algae, though pelagic forms are known to capture 

 other Protozoa and microcrustaceans. 



All species of Foraminifera manifest a more or less distinct 

 tendency toward a dimorphism: the megalospheric form with a 

 large proloculum and the microspheric form with a small proloc- 

 ulum (Fig. 157). The former is said to be much more numerous 

 than the latter. The microspheric form is multinulceate, in which 

 the nuclei are scattered without apparent order, and vary in size 

 proportionately with the size of the chambers. As the animal grows 

 the nuclei increase in number; around each of them a small island 

 of cytoplasm becomes condensed (c); uninucleate bodies thus 

 formed leave the parent body, and each secretes around itself a 

 shell which is much larger than the proloculum of the parent in- 

 dividual (d, e). To this proloculum, are added new chambers one 

 by one, as the organism grows (/) and at the same time the single 

 nucleus shifts its position, so that the latter is almost always in 

 the middle chamber. As the animal grows further, endosomes ap- 

 pear in increasing numbers in the nucleus which divides finally 

 into many nuclei (g). Each of these nuclei becomes the center of 

 swarmer. The swarmers leave the parent shell and undergo fusion 

 in pairs to produce zygotes (h-j). The zygote secretes a shell 

 around itself (a) and forms first a small proloculum, to which are 

 added many chambers (6). This is the microspheric form which in 

 some species appears to be unknown. 



More than 300 genera of extinct and living Foraminifera are 

 now known. Cushman distinguished 45 families. The present 

 work follows Cushman in recognizing and differentiating 44 fami- 



