io THE PROTOZOA-THE DAWN OF LIFE 



the Foraminifera of the Challenger Expedition, has classified them 

 in ten families. 1 



In the living Foram the bulk of the protoplasm is enclosed 

 within the shell, though part of it streams out from either the 

 large opening or from the numerous minute pores, in slender, 

 radiating, thread-like pseudopodia, which sometimes join and form 

 a living network. Diatoms, particles of animal or vegetable 

 matter, organisms even more minute than the Foram itself, may 

 become captured in the net and engulfed in the protruded proto- 

 plasm, and the soluble parts dissolved and assimilated, after the 

 manner already described in connection with the Amoeba. Soon 

 after the first simple shell has been formed a little mass of pro- 

 toplasm begins to project through the single large opening, or 

 through the scattered pores, as the case may be, and, increasing in 

 size, becomes enclosed in a shell like the original one, but 

 generally a size larger, and firmly connected with it, the cavities 

 of the two communicating with each other through the original 

 opening or pores. This process may be repeated again and again, 

 until, in place of a single speck of protoplasm enclosed in a single 

 shell, a composite structure has been built up, composed of many 

 particles of protoplasm, each having its own nucleus, each enclosed 

 in a shell, and all the shells firmly united together ; while the whole 

 of the particles of protoplasm are in continuity through the 

 apertures of communication. 



Although the shells of a large number of different species have 

 been most carefully described, there is need for further investiga- 

 tion into the processes of reproduction of the Foraminifera, but 

 multiplication by fission appears to be most typical. A method of 

 reproduction has been observed, in which the protoplasm inside 

 the shell divides up into a number of particles, and each of the 

 minute bodies so formed, instead of possessing pseudopodia, has 

 a single delicate flagellum or lasher, by means of which it moves 

 about. In the more typical fission process the nucleus may divide 

 into several parts, and round each of these products of nuclear 

 division a little mass of protoplasm gathers, and in this way young 

 individuals are formed, which in due course become enclosed in 

 shells and liberated from the parent. 



1 The name-giving types are Gromia, Miliolina, Astrorhiza, Lituolina, Textularia, 

 Chilostomella, Lagena, Globigerina, Rotalia, and Nummulites. 



