PROTOZOA RHIZOPODA. 149 



that " hundreds of them would hardly weigh a grain." 

 In some instances, the shell consists of only a single 

 chamber ; but usually there are a number of cells com- 

 municating with one another by minute openings. Some 

 of them are whorled like the shell of the nautilus, and, 

 on this account, were formerly believed to be minute 

 Mollusca. 



The animal which secretes those beautiful shells from 

 the sea-water seems to be of even a lower organization 

 than the Amoeba, as it does not contain any nucleus or 

 contractile vesicle. It is very extraordinary that such a 

 lowly creature should be able to execute such a beautiful 

 piece of workmanship. We have here an illustration of 

 the fact, that " life is the cause of organization, and not 

 the consequence of it." 



A foraminifer consists originally of a little mass of 

 jelly of a red or yellow colour. The outer coating of this 

 jelly secretes a shell consisting of a single chamber. As 

 the animal continues growing, it usually throws off buds, 

 each of which forms a fresh chamber. Thus, one of these 

 shells, minute as they are, generally contains a small 

 coloily of animals all united together into a living mass 

 by the canals which connect the chambers. In one of the 

 commonest groups (Globigerina), " when the process of 

 budding has produced a series of sixteen segments, the 

 next bud detaches itself, and begins to form a separate 

 shell." (Dr. Carpenter.) 



The pseudopodia, instead of being blunt processes, as in 

 Amoeba, are long threads of inconceivable fineness. These 

 threads interlace one another, forming what has been 

 termed a sort of " animated spider's web." The interior 

 jelly is constantly sending out fresh threads in search of 

 particles of food, and receiving those which are drawn 

 back. Sometimes the pseudopodia are emitted through 

 the mouth of the shell, but more generally through minute 

 apertures (foramina) in the walls of the chambers. On 

 this account the name Foraminifera has been given to 

 the whole group. Strictly speaking, the pseudopodia are 



