FERTILIZATION 593 



of the parasite Sphaerita in Amoeba Umax, as pictured by Chatton and 

 Brodsky (1909, Figs. 2, 3). The possibility of confusing sporulation of 

 Sphaerita with gamete formation in Amoeba is not too remote to be 

 considered; although, as Calkins has pointed out, a parasitologist is in- 

 clined to see parasites in everything, and the parasite explanation has 

 probably been over emphasized. The contradictory reports leave us in 

 the peculiar position of not being very sure of the life cycle of our best 

 known and most widely used protozoon, "the common laboratory 

 Amoeba." 



Fertilization processes have been described for a number of other 

 amoebae, including Pelomyxa palustris (Bott, 1907) and Sappinia 

 (Amoeba) diploidea (Hartmann and Nagler, 1908). Bott's account of 

 fertilization in Pelomyxa is unusual indeed. The nuclei of this multi- 

 nucleated Plasmodium extrude vegetative and generative chromidia into 

 the cytoplasm. The chromidia form secondary nuclei, which in turn cast 

 out the vegetative chromatin. The secondary nuclei, which now contain 

 only generative chromatin, undergo the first maturation division, in 

 which the chromosome number is reduced from eight to four. In the 

 second maturation division four chromosomes appear and split, so that 

 four go to each pole. Now each granddaughter nucleus divides into two 

 compact masses of chromatin and a vacuole is formed near-by. The 

 chromatin of the two masses then migrates into the adjacent vacuole, 

 in the form of minute granules. After receiving the chromatin, the vacu- 

 ole forms a membrane and becomes the definitive pronucleus of the 

 gamete. The pronuclei which have arisen in this unique manner ap- 

 propriate some cytoplasm and wander out as heliozoon-iike gametes, 

 which copulate in pairs to form zygotes. Each zygote grows into a new 

 multinucleate Pelomyxa. 



Aside from the peculiar role played by the vacuole in this maturation 

 process, which introduces a sort of modified autogamy into the cycle 

 just before the regular fertilization process, the cycle is worthy of further 

 examination. Formation of secondary nuclei from chromidia, which in 

 turn have resulted from the extrusion of chromatin from primary nuclei, 

 has been described in many Sarcodina, several Sporozoa, at least one 

 flagellate [Mastigella, see 2ho\t) and one ciliate {Trachelocerca phoeni- 

 copterus. Lebedew, 1909). 



Many protozoologists remain skeptical of the entire proposition of 



