NOVEMBEB 15, 1907] 



SCIENCE 



651 



tible features. They will, I think, agree 

 with me that were the powers of the micro- 

 scope increased many times, it is unlikely 

 that we should be very much wiser than we 

 now are. Evidence of a. different sort is 

 needed. 



Others by great ingenuity have tried to 

 penetrate a little deeper by making models 

 which in various ways can reproduce some- 

 thing of what is seen to occur, but the 

 features thus represented are those which 

 occur after the two centers are formed— 

 the consequences, that is to say, of the divi- 

 sion, not the division itself. 



That remains a phenomenon unparalleled 

 in the physical world, like consciousness, a 

 distinctive property of living matter. By 

 no confection of chemistry or mechanical 

 contrivance can we yet fit together a system 

 which wiU dichotomize and grow, dichoto- 

 mize and grow, repeating the process again 

 and again as long as certain materials are 

 supplied to it. 



The point on which I wish here to lay 

 the emphasis is the failure to conceive or 

 to represent the dichotomy. Heredity, as 

 we commonly see it, is much more than 

 that, but the dichotomy is the one feature 

 common to all its manifestations. I have 

 sometimes thought that in our investiga- 

 tions of the later and more special phenom- 

 ena of inheritance there is a danger of for- 

 getting that this is the essential fact. In 

 the visible rearrangement of the chromo- 

 somes, for example, in mitoses, occurrences 

 so tangible and striking are witnessed that 

 the observer can hardly avoid exclaiming, 

 ' ' This is the essential process of heredity, ' ' 

 or "Those chromosomes which I can watch 

 and count must be the physical basis of 

 hereditary likeness. ' ' Attractive and stim- 

 ulating as those wonders are to behold, the 

 essential is still beyond. Heredity began 

 in the explosion which impelled the chro- 

 mosomes on their courses. If it were pos- 

 sible to identify the chromosomes ever so 



clearly as the physical bearers of heredi- 

 tary characters, the problem of the division 

 would remain, and I am strongly led to 

 expect that it must be in some new light 

 on the causation of the division that the 

 way to attack the essential problem will be 

 found. In this expectation I am glad to 

 find myself in agreement with Dr. Loeb, 

 whose stimulating address we heard yester- 

 day. The researches which he has so suc- 

 cessfully inaugurated have brought the 

 problem of cell division at last within the 

 range of experiment; and if the nature of 

 the explosion remains still inscrutable, 

 Loeb's work has shown how the charge 

 may be fired. 



In our deliberations I anticipate that the 

 more immediate question, whether the chro- 

 mosomes are or are not the bearers of 

 hereditary characters, will be fully debated. 

 Without presuming to a definite opinion 

 on this question, I venture to state what 

 seem to me formidable difficulties in the 

 way of this expectation. If the chromo- 

 somes were directly responsible as chief 

 agents in the production of the physical 

 characteristics, surely we should expect to 

 find some degree of correspondence be- 

 tween the differences distinguishing the 

 types, and the visible differences of number 

 or shape distinguishing the chromosomes. 

 So far as I can learn, no indication what- 

 ever of such a correspondence has ever 

 been found. Besides this, although no very 

 thorough investigation of the chromosomes 

 of somatic structures has yet been made on 

 an extensive scale, I believe that definite 

 cytological distinctions between the nuclei 

 of the various tissues of the same body 

 have not been detected. If chromosomes 

 were the chief governors of structure, sure- 

 ly we should find great differences between 

 the chromosomes of the various epithelia, 

 which differ greatly in their structure and 

 properties. As these cytological differ- 

 ences have not been found consistently 



