Heredity. 
217 
in producing the garden pansy from the wild form, Viola tricolor, 
in the course of eighteen years, is regarded as proof of a change in 
the germ-plasm. 
It is admitted that a small number of observations made upon 
man and the higher animals seem to prove that injuries or mutilations 
of the body can, under certain circumstances, be transmitted to the 
offspring. A cow which had accidentally lost her horn produced a 
calf with an abnormal horn ; a bull which had accidentally lost his 
tail, from that time begat tailless calves ; and so on. The great 
difficulty in dealing with such cases arises from their doubtful 
authenticity. 
To sheep-breeders there is a certain ndivett about the following 
statement : — 
" Professor Kiihn, of Halle, pointed out to me that, for practical reasons, 
the tail iu a certain race of sheep has been cut off during the last hundred 
years, but that, according to Nathusius, a sheep of this race without a tail, or 
with only a rudimentary tail, has never been born. This is all the more 
important because there are other races of sheep in which the shortness of the 
tail is a distinguishing peculiarity. Thus, the nature of the sheep's tail does 
not imply that it cannot disappear." 
Another illustration is afforded by the rook, which digs into the 
earth in its search for food, and in this way the feathers at the base 
of the beak are rubbed off, and can never grow again because of the 
constant digging. Yet this peculiarity, which has been acquired 
again and again from time immemorial, has never, it is said, led to 
the appearance of a newly -hatched rook with a bare face. 
Since the death of Darwin, no such important questions have 
been raised as those in this volume ; and though, to the younger 
school of English biologists, Weismann's conclusions may appear 
inconsistent and contradictory, yet his researches cannot fail to exer- 
cise an influence on the future development of biological science. 
Many of the illustrative cases cited are of extreme interest. 
As regards the duration of life, the horse and bear attain an age of 
50 years at the outside ; the lion lives about 35 years, the 
wild boar 25, the sheep 15, the fox 14, the hare 10, the squirrel and 
the mouse 6 years. On the other hand, whales live for some 
hundi-eds of years, and elephants for 200 years. The long life of birds 
is regarded as a compensation for their feeble fertility and for the 
great mortality of their young. Much information of direct value 
in devising means for coping with insect-pests is discoverable in the 
pages on duration of life in insects, the general rule being enunciated, 
that this duration is directly proportional to the number of eggs 
and to the time and energy expended in oviposition. That the 
saw-tlies, so familiar to us as destructive pests, were the probable 
ancestors of bees and ants is a circumstance of high interest. The 
duration of the larval life in insects is determined chiefly by the 
nature of the food, and the ease or difficulty with which this can 
be procured. The larva of the bee becomes a pupa in five to six 
days; but then it is fed with materials (honey and pollen) of high 
