D. J. SCOURFIELD ON MENDELISM AND MICROSCOPY. 407 



evidence seemed at one time to show that two or more pairs 

 of characters might under some conditions become so linked 

 together as to be inherited as a single pair, although separating 

 again under other conditions. It is, however, not quite certain 

 at present whether this assumption is really needed, for it has 

 been found possible to explain some at least of the cases— e.g. the 

 combs of fowls —iu a more direct manner, as indicated above. 

 There seems nothing unreasonable in supposing that several pairs 

 of characters may at one time act as a single pair, and then, 

 under other circumstances, break up again. Many cases of what 

 seem to be linked characters — the so-called correlated characters, 

 in fact — are known, although these appear never to break up into 

 independently heritable units. Until, however, it is shown to be 

 absolutely necessary, it will probably be better not to assume the 

 existence of compound allelomorphs or hereditary radicals, as they 

 might be called. 



Having now completed the survey of Mendel's experiments 

 and some of the more recent developments on the same lines, we 

 can pass on to a consideration of the relation of Mendelism to 

 microscopical work. There are, indeed, many points of contact 

 between the two, but I think they may all be grouped under 

 three main headings. Firstly, there is the very evident connection 

 between Mendelism and cytological investigation, especially that 

 branch which deals with the germ-cells ; then there is the relation 

 which arises from the fact that many naked-eye characters are 

 founded upon microscopical elements ; and, lastly, there is the 

 possibility of using microscopic organisms for experimental 

 work in the same way as Mendel used his peas, beans, etc. It 

 will be convenient to take these three points of view in the 

 order mentioned. 



^Yith regard to the first it is at once apparent that the position 

 of affairs in 1900, when Mendel's paper was rediscovered, was 

 very different to what it was in 18G5, when the paper was 

 published. An enormous advance had been made in the interval 

 in the knowledge of the microscopical structure of plants and 

 animals, especially in connection with cell-structure and cell- 

 division. One of the earliest questions that arose, therefore, after 

 the rediscovery of the paper, was, how does this new doctrine fit 

 in with what is now known about the maturation, fertilisation, 

 and division of the germ-cells ? 



Jourx. Q. M. C., Series II.— No. 59. 29 



