Packard.] 
508 
[Feb. 19, 
when subjected during several generations to any change whatever 
in their conditions, tend to vary.” Farther on he refers to the gen- 
eral arguments, which appear to him to have great weight, “ in favor 
of the view that variations of all kinds and degrees are directly or 
indirectly caused by the conditions of life to which each being, and 
more especially its ancestors, have been exposed ” (p. 241), and 
he finally concludes : u Changes of any kind in the conditions of life, 
even extremely slight changes, often suffice to cause variability. 
Excess of nutriment is perhaps the most efficient single exciting 
cause ” (p. 258). 
When in Mesozoic, or possibly still earlier times, caterpillars be- 
gan to migrate from herbaceous plants to trees, they experienced 
not only some change, however slight, in the nature of their food, 
but also a slight climatic change, so to speak, involving a change 
in the temperature. Insects living in trees or shrubs, several or 
many feet above the ground are certainly exposed to a more even 
temperature, as it is colder at night even in midsummer within a 
few inches of the ground, say about a foot, the usual height to which 
grasses and herbs grow. The changes, therefore, by day and night 
are greater at the surface of the ground than among the leaves and 
branches of a tree. Moreover forests, not too dense for insect-life, 
with glades and paths to admit the sunlight and heat, must neces- 
sarily have a more even temperature and be less exposed to cool 
winds, and less subject to periods of drought than grassy fields. 
There is also a less free circulation of air among grasses and herbs, 
which may be more or less matted and lodged after heavy rains, 
growth and metabolism, and the expenditure of energy under such wholly new and re- 
stricted conditions as to render it almost certain, as he thinks, that these factors have 
something to do with the development of the enormous and abnormally lengthened 
pectoral, ventral, dorsal, double anal and caudal fins of his stock. Some of the races 
of these fishes have obviously been affected in appearance by abundant feeding, as is 
attested by their short, almost globular bodies, protuberant abdomens, and greedy 
habits as I have observed in watching examples of this short-bodied race living in 
Dr. Wahl’s aquaria. In these last instances we are brought face to face with modifi- 
cations occiu*ring in fishes under domestication which are infinitely in excess, morpho- 
logically speaking, of anything known amongst any other domesticated animals. That 
the abundant feeding and exposure to a uniform temperature during the whole year, 
and confinement in comparatively restricted quarters have had something to do with 
the genesis of these variations, through an influence thus extended upon the metabol- 
ism affecting the growth of certain parts of the body, which have tended to become 
hereditary, there can scarcely be any doubt” (American Naturalist, Jan., 1890). 
Darwin states that in India several species of fresh-water fishes “ are only so far 
treated artificially, that they are reared in great tanks; but this small change is suffi- 
cient to induce much variability (Variation of Animals>nd Plants under Domesti- 
cation, II, 216). 
