PROTOZOA. 25 



specialized genera of Protozoa tend to strengthen this 

 hypothesis. 



It is probable, although it is not yet proved, that 

 Amoeba proteus forms swarm-buds in the shape of little 

 Amoebae. 



PL 9 is instructive since it places before the student a 

 simple organism capable of performing in a simple way 

 the vital functions of the most specialized animals. 



Many interesting differentiations of structure are shown 

 in other species of Amoeba. The marine Amoeba (A. 

 obtecta) crawls with extreme slowness. According to 

 Gruber these Rhizopods do not exhibit any tendency to 

 undertake migrations, and therefore when the conditions 

 are favorable they lie together in great numbers and thus 

 form regular societies. 1 



In Amoeba polypodia M. Schultze (PL 10, figs. i-8a), 

 which may have one or several nuclei, the pseudopodia 

 are numerous, and are more equal throughout their length, 

 approaching the thread-like organs of many Foraminifera. 

 The process of fission is shown in figs. i-8a, which illus- 

 trate more clearly the different stages of development 

 than preceding figures. The specimen observed had one 

 nucleus. The division of this organ took place in one 

 minute and a half, and that of the body in eight and a 

 half minutes, so that ten minutes were required for the 

 whole process. Figs. 2-8a are drawn in outline, showing 

 the division of the nucleus and protoplasmic body and 

 also the increase in the -number of vacuoles. 



There are organisms closely related to these Amoebae 

 which seem to throw light on the origin of the flagel- 

 lum, and to point to the probability that certain Rhizo- 

 pods have given rise to the Mastigophora (^= Flagellata.) 

 According to Calkins, 2 however, there is no conclusive 



1 Zeitschr. f. wiss. Zool., XXXVIII, 1883, p. 56. Engl. transl., 

 Ann. and Mag. Nat. Hist., (5), XI, 1883, p. 276. 



2 The Protozoa, 1901, p. 105. (Columbia University Biological 

 Series, VI.) 



