DARWIN MEMORIAL CELEBRATION 
7 
2. Fluctuating variations in one species of a clam-like animal, Tellina. 
3. Slight differences between and among different types of a kind of 
terrestrial snail, Helix. 
4. Variable shells of the common scallop, Pecten, arranged also to 
show the general law of variation. 
5. Varieties of the Tiger Cowry, from Malaysia. 
6. “Mutations,” or wide “deviations from type,” in several species 
of birds. 
C 
STRUGGLE FOR EXISTENCE 
The natural rate at which living organisms multiply is so rapid that only 
a small portion of the individuals which begin life can survive in the struggle 
for existence. The elimination of the unfit and the survival of only the fit 
are the results of the many-sided warfare in which all organisms must engage 
because of over-multiplication. Nevertheless, a form that has been intro¬ 
duced into a new locality may spread with remarkable rapidity, owing to a 
partial suspension of selection brought about by the exemption of the form 
from the severe struggle for existence under the conditions of its original 
habitat. 
Illustrations 
1. A demonstration of the results of the normal rapid rate of multi¬ 
plication under the supposition that no elimination takes place 
— results which could not be produced in nature. 
2. The Water Hyacinth, a plant which has been introduced into 
Florida, a new habitat, where it has multiplied at such a rate 
as to choke the streams. 
3. A map showing the area of distribution of the English Sparrow 
in the year 1S86, twenty-two years after its introduction into 
North America. 
4. A map showing the spread of the Potato-Bug, during successive 
decades. 
5. A demonstration of the struggle for existence of young plants 
grown from seeds planted in areas that overlap. 
6. Photographs of the conditions in forests, where low-shrubbery is 
prevented from growing because of the lack of light in the 
shade of the large trees. 
7. A group showing the Meadow-Mouse and its natural enemies 
and food-organisms; a demonstration of the complexity of the 
struggle for existence. 
