JENNINGS: CHANGES IN HEREDITARY CHARACTERS 281 



of the bench magma must proceed aphrolithically. Supposing 

 the cumulo-domes of Bogoslof and Pelee to be essentially aphro- 

 lith, it is a matter of great interest to determine whether any 

 dermolithic flow, however small, took place in those magmas. 

 At Soufriere in St. Vincent, and also on Bandaisan, there are 

 aphrolithic blocks of fresh rock quite distinct from the angular 

 fragments, and apparently representative of the subterranean 

 magmas which produced the explosions. 



If these terms are adopted, it is hoped that they will not be 

 changed in English to the -lite termination, as Harker 2 insisted 

 on doing for "batholite," etc. The -lite syllable is needlessly 

 confusing, on account of the innumerable rock and mineral 

 names so ending. Harker's contention is that "-lith" is con- 

 tinental and not English, but this is disproved by such a word 

 as monolith, which is accepted English of Greek derivation. 



GENETICS. — Observed changes in hereditary characters in re- 

 lation to evolution^ H. S. Jennings, Johns Hopkins Uni- 

 versity. 



The problem of the method of evolution is one which the bi- 

 ologist finds it impossible to leave alone, although the longer 

 he works at it, the farther its solution fades into the distance. 

 The central point in the problem is the appearance, nature, and 

 origin of the heritable variations that arise in organisms; the 

 changes that occur in the hereditary constitution. I have for 

 a long time been studying the appearance of heritable variations 

 in certain lower organisms. Having satisfied myself as to the 

 nature of the variations that arise in the creatures that I have 

 studied, I have looked about to see what other workers have 

 found ; and to determine whether any unified picture of the 

 matter can be made. Can we bring these facts which experi- 

 mental work has brought out into relation with the method of 

 evolution? Can we say that they exclude any particular theory? 



2 Harker, A. Natural History of the Igneous Rocks. 



1 A lecture delivered before the Washington Academy of Sciences, March 15, 

 1917. 



