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SCIENCE 



[N. S. Vol. XXVI. No. 672 



and the creation of this section and of 

 sections for experimental zoology and 

 cytology testifies to the existence of new 

 methods and new hopes. 



Limitations of the animal classes do not 

 trouble us. We take facts wherever we 

 can find them. We are botanists to-day, 

 zoologists to-morrow. The widening of in- 

 terest which the study of heredity is bring- 

 ing into modern zoology must prove a 

 great benefit to the science. 



When morphology was a new idea, 

 everything was sacrificed to its pursuit. 

 Physiology, systematics, aU were discarded 

 as useless lumber. Let us not repeat that 

 short-sighted mistake. In the wider sur- 

 vey which we are attempting we shall need 

 all these things. If we are to understand 

 rightly the phenomena of specific differ- 

 ence—to take that problem only— we shall 

 be glad of anything that the systematist 

 can tell us, and of many deductions of 

 pure physiology. 



The study of heredity and variation— of 

 genetics, to use our modern term— is it- 

 self a purely physiological inquiry, and 

 as such it must range itself among other 

 physiological inquiries; standing next be- 

 side, and looking constantly for support to, 

 physiological chemistry. 



The accidents of development which dis- 

 sociated zoology from physiology were, as 

 we are beginning to perceive, a misfortune, 

 though perhaps an inevitable one. The 

 botanists are happy in that their smaller 

 dimensions have prevented such disrup- 

 tion. .But let us hope that the dynamics 

 of the zoological system may admit of the 

 retention of that part of physiology which 

 still adheres. Genetics will grow to be a 

 big sphere one day; but may it never 

 break off from the parent body whether as 

 satellite or as sun. 



Let us now examine the task which lies 

 before us as students of genetics. Vari- 



ous descriptions of our objects may be 

 made, referring to the phenomena of 

 heredity and variation; their bearing on 

 the theory of evolution, or on the origin 

 and destinies of races. Stripped of all 

 that is superfluous and of all that is 

 special to particular cases, genetics stand 

 out as the study of the process of cell- 

 division. For if we had any real knowl- 

 edge of the actual nature of the processes 

 by which a cell divides, the rest would be 

 largely application and extension. It is in 

 cell-division that almost all the phenomena 

 of heredity and variation are accomplished. 

 Nothing is more easy than to witness this 

 process. We ,may behold its minutest 

 visible details when we please and as often 

 as we please, and stiU no one has even a 

 plausible guess as to the essential nature 

 of the process. Two centers form: the 

 parts collect round each. The two halves 

 withdraw; or, if we may commit ourselves 

 so far, repel each other, and there are then 

 two cells instead of one. The likeness of 

 those two cells we call heredity; their dif- 

 ference we call variation. If the two cells 

 remain constituent parts of one body, we 

 may speak of their likeness as symmetry 

 or repetition; and their points of unlike- 

 ness we then call differentiation. But how 

 the two centers were formed, not to speak 

 of why, and how they came to separate, 

 we have no surmise. Still less can we con- 

 jecture what it was that decided the dis- 

 tribution of differences between the two 

 halves. No phenomenon of common life 

 is so obscure. 



By suitable means many of the finer de- 

 tails can be watched, but the most meticu- 

 lous observation has failed to disclose the 

 essential truth which must yet be so near. 

 I am speaking in a country where by the 

 determination of vigorous observers a great 

 school of cytologists has arisen who have 

 greatly added to knowledge of the percep- 



