The Problem of Synapsis. 271 



size and shape as follows : a and a are rod-like and equal ; two 

 pairs, yS and ^', 7 and 7, are Y-shaped and equal ; one pair, S and h', 

 are minute and spherical ; while the fifth pair is unequal, ajand y. 

 Reduction takes place in the formation of the sperms, and the 

 second spermatocyte has the constitution a or a' -f , y8 or yS' -f , 

 7 or 7' + , S or h' ■\', X or y. Assuming that, as in all the closely 

 allied insects, x is equally paired in the female, it follows that the 

 gamete has one representative of each pair of chromosomes in the 

 gametogonial cells ; and if it is legitimate to assume that the 

 chromosomes of the latter correspond individually to those of the 

 zygote, it is clear, since the zygote is the product of the union of 

 two gametes, that the process of " reduction " involves the resolu- 

 tion of chromosome pairs into their maternal and paternal com- 

 ponents. The debatable implication of this argument is the 

 assumption that the chromosomes of one cell generation individu- 

 ally correspond to those of another. As is well known, the 

 chromatin organization of an ordinary resting nucleus exists in a 

 reticulate condition, so that it is not possible to settle by imme- 

 diate inspection whether the chromosomes are temporary and in- 

 constant aggregates of chromatin particles, or whether on the other 

 hand to decide in favour of a definite structural continuity of the 

 former as opposed to an interpretation of a more remote character. 

 Upon this decision the elaborate body of doctrine embodied in 

 *' the chromosome hypothesis " logically rests. 



The considerations in favour of the view that each chromosome 

 of the prophase corresponds structurally to a similarly constituted 

 chromosome in the preceding telophase may be summarized as 

 follows: — {!) Actual continuity occurs in certain plants; ''pro- 

 chromosomes " were first observed by Schwarz (1892) and Zacharias 

 (1895) ; they have been recently studied by Overton, Eosenberg and 

 Stout (1913). (2) The transition of the chromosomes of the telo- 

 phase into the reticulate condition, and the emergence of the 

 prophase from this state studied by Overton in Podophyllum, 

 Digby (1919) in Osmunda; also Boveri's work on the relation of the 

 chromosomes to the orientation of the reticulum in the curiously 

 lobed nuclei of Ascaris, seem to indicate clearly that the reticulum 

 is itself a complex of "unit reticula," corresponding to the chromo- 

 somes themselves. (3) The numerical relations exhibited in the 

 behaviour of the chromosomes in mitosis always fulfil the expecta- 

 tions that would be anticipated on the assumption of persistent 

 individuality not only in normal reproduction but also in cases of 

 polyspermy (Boveri), and of hybrids from parents with complexes 

 that are numerically unlike (Federley). (4) The character of the 

 complex when it exhibits heteromorphism is only such as could be 

 expected if the chromosomes maintained their individuality intact 

 from one generation to another. This is very arresting in the case 

 of hybrids (Federley, Baltzer) of parents whose chromosomes are 



