762 EEPOET— 1889. 



would not be quite the same. Variations in structure, and to some extent also in 

 tbe construction of parts, wonld arise, and the unlike would be produced. 



In this connection it is also to be kept in mind that in the higher organisms, 

 and, indeed, in multicellular organisms generallj', an individual is derived, not from 

 one parent only, but from two parents. AVeismann emphasises this combination 

 as the cause of the production of variations and the transmission of hereditary- 

 individual characters. If the proportion of the particles derived from each parent 

 and the forces which they exercise were precisely the same in any individual case, 

 then one could conceive that the product would be a mean of the components pro- 

 vided by the two parents. But if one parent were to contribute a larger proportion 

 than the other to the formation of a particidar organism, then the balance would 

 be disturbed, the offspring in its character would incline more to one parent than 

 to the other, according to tbe proportion contributed by each, and a greater scope 

 for the production of variations would be provided. These differences would be 

 increased in number in the course of generations, owing to new combinations of 

 individual characters arising in each generation. 



As long as the variations which are produced in an organism are collectively 

 within a certain limitation, they are merely individual variations, and express the 

 range within which such an organism, though exhibiting differences from its 

 neighbours, may yet be classed along with them in the same species. It is in this 

 sense that I have discussed the term A^ariability up to the present stage of this 

 address. Thus all those varieties of mankind which, on account of ditferences in 

 the colour of the skin, we speak of as the white, black, yellow races and red-skins 

 are men, and they all belong to that species which the zoologists term Homo sapiens. 



But the subject of Variability cannot, in the present state of science, be confined 

 in its discussion to the production of individual variations within the limitations 

 of a common species. Since Charles Darwin enunciated the proposition that 

 favourable variations would tend to be preserved, and unfavourable ones to be 

 destroyed, and that the result of this double action, by the accumulation of minute 

 existing differences, would be the formation of new species by a process of natural 

 selection, this subject has attained a much wider scope, has acquired increased 

 importance, and has formed the basis of many ingenious speculations and hypo- 

 theses. As variations, when once they have arisen, may be hereditarily transmitted, 

 the Darwinian theory might be defined as Heredity modified and influenced by 

 Variability. 



This is not the place to enter on a general discussion of the Darwinian theory, 

 and even if it were, the time at our disposal would not admit of it. But there 

 are some aspects of the theory which would need to be referred to in connection 

 with the subject now before us. It may be admitted that many variations which 

 may arise in the development of an individual, and which are of service to that 

 individual, would tend to be preserved and perpetuated in its ofl'spring by here- 

 ditary transmission. But it is also without question that variations which are of 

 no service, and, indeed, are detrimental to the individual in which they occur, are 

 also capable of being hereditarily transmitted. This statement is amply borne 

 out in the study of those important defects in bodily structure which pathologists 

 group together under the name of Congenital Malformations. I do not require to 

 go into much detail on this head, or to cite cases in which the congenital defect 

 can only be exposed by dissection, but may refer, by way of illustration, to one or 

 two examples in which the defect is visible on the surface of the body. The 

 commonest form of malformation the hereditary transmission of which has been 

 proved is where an increase in the number of digits on the hands or feet, or on 

 both, occurs in certain families, numerous instances of which have now been put 

 on record. But in other families there is an hereditary tendency to a diminution 

 in the number of digits or to a defect in the development of those existing. I 

 may give an illustration which occurred in the family of one of my pupils, the 

 deformity in which consisted in a shortening or imperfect growth of the meta- 

 carpal bone of the ring finger of the left hand, so that the length of that finger 

 was much below the normal. This family defect was traceable throughout six 



