1884.] Growth, its Conditions and Variations. 1091 
starvation, accident, the violence of foes and all the external con- 
ditions which oppose individual life continuance. Therefore some 
degree of reproductive activity is necessary to the continued exis- 
tence of any animal race, and it is probable that any degree of 
this activity is incompatible with continuous individual life. 
The shedding of wandering cells appears to take place through- 
out the whole life of the higher animals. They may be found as 
amceboid corpuscles in the blood at all periods of growth. Only 
in the lowest forms, however, can they be developed as germs of 
new individuals at all periods. In all forms above the lowest 
some organ for their temporary reception must be first produced, 
in which the earlier stages of development can be passed, since 
the higher the animal the more unsuited is its germ for immediate 
self-nutrition, When the sexes become separate this grows more 
necessary, and individual development must pass through certain 
phases ere the organs necessary for reproduction are unfolded. 
Over this unfoldment of organs the nutritive conditions exert an 
important influence. Very active nutrition acts to check struc- 
tural development. The writer has treated this subject at length 
in a former paper, and need simply here refer to the case of 
insects-in which structural development is retarded during 
the active nutrition of the larval stage, and is only actively 
resumed during the innutrition of the pupa stage. Thus with 
insects the conditions requisite to reproduction are only com- 
pleted in the imago stage of development. ; 
It is not alone reproduction that checks growth, since repro- 
duction, under certain conditions, might long continue without 
that cessation of growth which usually accompanies sexual 
maturity. But reproduction, to be effective, must be of such a 
character as to assure the preservation and mature development 
of at least two offspring to every two parents. This can be done 
in one of two ways, either by the production of germs in great 
numbers, if they are left to take their chances of destruction by 
enemies or hostile natural conditions, or by the production of 
er germs, which are kept under parental protection until the 
young are able to shift for themselves. Both these processes are 
exhaustive of vitality. In the case of fish, which shed into the 
Water immense numbers of sperm and germ cells, the p hysica! 
Strength is reduced by great abstraction of vital material. In the 
Growth and Development, AMERICAN NATURALIST, July, 1883. 
VOL. xyn1.—no. xz, 69 : 
