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THE AMERICAN NATURALIST [Vol. XLII 



phase of the smallpox organism. But between this parasite and 

 the chromidia of Amoeba proteus there is not the slightest trace 

 of resemblance. 



In the earlier paper it was supposed that the chromidia stage 

 is only the antecedent of the later gamete formation and that 

 conjugation of gametes is the method of ferl i I iz;it ion. In a later 

 paper Calkins" described some further studies made upon the 



balsam, embedded in pa ratline and sectioned. The supposed 

 chromidia granules were then described as minute secondary- 

 nuclei which unite two by two, each couple giving rise to a 

 reproductive body similar to a sporoblast. There were many 

 gaps in this later account of fertilization and much remains to 

 be done before the fertilization of Amahn protrus is established, 

 but these later observations indicate a fundamental agreement 



is autogamous. In Amuba proh us the original nucleus of the 

 cell divides repeatedly, the resulting nuclei break down into 

 fragments, each of which is a complete gametic nucleus. Fertil- 



It must not be forgotten in comparative studies of this kind 

 that the organisms are widely different and that the expression 

 of the fundamental biological activity underlying chromidia 

 and fertilization is worked out in widely different ways. This 

 obvious and trite observation has not been heeded in a recently 

 published work on parasitic rhizopods by E. L. Walker. 10 Car- 

 ried away, apparently, by success in raising aimeboid organisms 

 jn large quantities by using artificial culture media recommended 

 by Musgrave and Clegg, "Walker has allowed to slip away a 

 valuable opportunity to contribute something new to our knowl- 

 edge of intestinal forms of rhizopods. while, on the other hand. 



