PROTOZOAN GERM PLASM 



57i 



Fig. 3. 



After Calkins. 



cells which now undergo, separately, the later stages of development. 

 These stages consist in the division of the fertilization nucleus and new 

 formation from the division products, of the new macronucleus and the 

 new micronucleus (Fig. 4). 



After such a process of fertilization it would seem that the indi- 

 viduals are pretty much as they were before except for the complete 

 reorganization of the nuclear apparatus, and there is a certain justifica- 

 tion for the Weismann conception. But the phenomena in Paramecium 

 and allied forms, like their cell differentiations, are highly specialized 

 and are unlike the fertilization processes in the majority of Protozoa. 



The enormous group of Sarcodina, including more than four 

 thousand species of Eadiolaria and some thousand or more species of 

 Foraminifera, Heliozoa and Ehizopods, presents a fairly uniform picture 

 of the germ plasm and the processes of fertilization. For purposes of 

 illustration and comparison I will describe two types selected from this 

 great group of forms — one a marine foraminiferon, Polysiomella, crispa, 

 the other a common fresh-water rhizopod Arcella vulgaris. 



So far as known, each species of Foraminifera exists in two forms 

 known as the microsphaeric and the megalosphgeric forms, so called 

 because of the small and large size of the central or initial chamber of 

 the shell (Figs. 5 and 6). These two forms correspond with the asexual 

 and the sexual generations of metagenetic hydrozoa, the microsphasric 



