. Evolution and animal life; an elementary discussion of facts, processes, laws and theories relating to the life and evolution of animals . rily what isknown of the chemical and physical make-up of is actually known, by chemical analysis and earnestmicroscopic peering, of this structural make-up is wholly in-sufficient to serve as a satisfactory basis of any causomechani-cal explanation of protoplasmic properties. Although someof the simpler capacities of protoplasm, as its motion, itstaking up of outside substances (feeding), etc., have been tosome degree explained by seeing
. Evolution and animal life; an elementary discussion of facts, processes, laws and theories relating to the life and evolution of animals . rily what isknown of the chemical and physical make-up of is actually known, by chemical analysis and earnestmicroscopic peering, of this structural make-up is wholly in-sufficient to serve as a satisfactory basis of any causomechani-cal explanation of protoplasmic properties. Although someof the simpler capacities of protoplasm, as its motion, itstaking up of outside substances (feeding), etc., have been tosome degree explained by seeing in them direct physicochem-ical reactions to external stimuli or conditions, practicallynothing has been really accomplished as yet toward a mechani-cal explanation of such more complex or unusual capacitiesas irritability, assimilation, and reproduction. This last func-tion of protoplasm is in a way its most apparently hope-lessly inexplicable property. And this is especially so whenthe reproduction is of the sort peculiar to the germinal proto-plasm; that is, where the reproducing protoplasmic mass does 248 EVOLUTION AND ANIMAL LIFE. •.- not simply divide and thus make two masses each capable ofthe growth and change necessary to make it like the parentmass, but where the parent mass (a fertilized egg cell, or a sexualegg or bud cell) can grow and develop into a highly complexmany-celled new organism of type like that from which theparent germ plasm was derived. The special capacities, there-fore, of germ plasm have furnished for centuries, and do to-day, the great problem of biology(next to that provided by theexistence of life itself). If we cling to a belief thatin some way, after all, the ex-planation of the general proto-plasmic and special germ plasmcapacities lies in an unusualcombination of structure andplay of familiar form of energythrough the structure, we areat once forced to assume astructural make-up of proto-FIG. 144.—Egg ceil of a sea urchin, TOXO- plasm an
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