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THE AMERICA N NA TU BALI ST [Vol. XLIII 



strains. These phenomena may be compared to various 

 anomalies which take their origin in the soma. The em- 

 bryo in its development is liable to certain accidents 

 resulting in the production of teratological phenomena 

 such as hare-lip, double formations, anencephaly and 

 many others. These anomalies fall into certain classes 

 and in many cases can be attributed to particular defects 

 of development. The germ plasm also may be regarded 

 as liable to certain classes of accidental modifications 

 which produce heritable variations of more or less clearly 

 defined types. No one would think of attributing anom- 

 alies of somatic origin to the development of a new kind 

 of organic unit. If the same mutation appears time after 

 time, would it not be more reasonable to suppose that it 

 arose after the fashion of somatic anomalies than that it 

 depended upon the creation each time of the same kind 

 of a new pangen? The fact that mutations can be in- 

 duced through the influence of the environment certainly 

 favors such a view. Tower found that in Leptinotarsa 

 certain variations or mutations arose repeatedly in inde- 

 pendent strains and that by subjecting the beetles to un- 

 usual conditions during the period of active development 

 of their germ cells the proportion of these sudden varia- 

 tions could be very greatly increased. The variations 

 thus produced belonged to a few well-marked types, and 

 while it would be hazardous to set bounds to the possible 

 number of mutants the species may produce, it is probable 

 that the number is subjected to a certain limitation im- 

 posed by the peculiar organization of the germinal sub- 

 stance. 



The selection of variations by the germ plasm may be 

 illustrated by some observations of Jennings upon inherit- 

 ance in Protozoa. In a few specimens of Paramecium 

 it was noticed that the body was furnished with a spine- 

 like excrescence. During fission the spine was trans- 

 mitted to but one of the individuals, the acquired peculi- 

 arity not arising on the other. In one case the spine was 

 transmitted through twenty-one generations, when the 



