THE HISTORY OF ANATOMICAL SCIENCE 325 



In trying to form a judgment of the value 

 of the explanation offered, it is a necessary 

 preliminary to consider what there was to ex- 

 plain. 



Among the animals with which we are familiar, 

 proliferation, or the production of offspring, inva- 

 riably implies the concurrence of two parents, a 

 father and a mother. We are, therefore, naturally 

 led to regard this method of proliferation as the 

 rule, and any other as an exception. But, as we 

 have seen, if our daily experience had been 

 derived from many of the lower animals and 

 plants, we might just as well have been led to 

 think sexless proliferation the rule, and the 

 other the exception. Whatever the outward 

 form of the process of proliferation, in sub- 

 stance it always comes to the same thing. It 

 is the detachment of a parcel, A, of the living 

 substance of the parent, which either before, or 

 after, detachment evolves into a complete, physio- 

 logically independent, organism. There are in- 

 numerable cases in which this process takes place, 

 in virtue of the autonomous activities of the living 

 substance of an organism. The progeny in this 

 case is a detached fragment of A, and nothing 

 else. Why is it that, in equally numerous other 

 cases, a parcel of the same kind may be similarly 

 detached from A, but does not evolve, unless an- 

 other parcel, B, of living substance, derived from 

 the same, or another, organism, not merely comes 



