9 2 



THE PROTOZOA 



disintegrated, the digestible portions being transformed into a sort 

 of chyle which is distributed throughout the protoplasm. The gastric 

 vacuole with its undigested residue is gradually left behind like a 

 loaded contractile vacuole, until finally it is expelled to the outside 

 (Amceba). The Sarcodina, apparently, digest mainly proteids, some 

 forms of starch, and fats remaining unchanged (Meissner, '88 ; Green- 

 wood, '80; Stole, 'oo ). 



G. REPRODUCTION 



The Sarcodina reproduce mainly by simple division or spore-for- 

 mation, either in the free state while active, or when quiet in the 

 encysted state. The simplest form, consisting of a mere bipartition 

 of the protoplasm and of the essential body-contents, occurs when the 

 body is so large that it becomes unwieldy and it divides from sheer 

 inertia. A well-known example is that of the division of Amoeba 

 poly podia {Dactylospluzra, F. E. Schultze). Here, as in all cell-divi- 

 sions, the nucleus divides first, the body then separating into two parts. 

 Simple division becomes more complicated when the organism is 



Fig. 51. Microgromia socialis Hert. [HERTWIG.] 



Division takes place within the shell, and one of the daughter-individuals migrates, forming a 

 new shell. 



provided with an outer coating or test, although in the simplest of 

 such cases, where the coating is flexible and plastic, as in Vampyrclla> 

 the process involves only the partition of the outer membrane. When 

 the outer covering becomes hard and firm by impregnation with chi- 

 tinous, silicious, calcareous, or horny materials, the operation is more 

 complicated. The organism, while still within the shell, may divide 

 by longitudinal division, one of the daughter-individuals then migrat- 

 ing from the parent shell and, after a longer or shorter time, settling 

 down and secreting a new shell for itself, the other daughter-indi- 



