TRANSACTIONS OF SECTION K. 755 



step in advance as to the nature of reduction was made by Montgomery, in 1901, 

 when be put forward the theory, now generally accepted, that in synapsis maternal 

 and paternal chromosomes unite in pairs, and are later separated by the reduction 

 division, which thus divides the somatic chromosomes into two groups. In the 

 life-cycle of the organism we have thus : Conjugation of maternal and paternal 

 cells, somatic divisions, and conjugation of maternal and paternal chromosomes. 

 The later observations of Montgomery and those of Sutton, McClung, Boveri, 

 Baumgartner, Wilson, &c., on the diflference in size, in form, and in physiological 

 function of the chromosomes, all point to the probability that the somatic nuclei 

 contain two parallel series of chromosomes, derived respectively from the maternal 

 and the paternal sides ; and that in synapsis there is a conjugation of ' homo- 

 logous' chromosomes, which are later separated in the reduction division. The 

 exact mode of conjugation of the chromosomes is disputed, but observers are 

 generally agreed as to the end result — the separation of whole somatic chromo- 

 somes. The interest of this view is that it is in general agreement with Mende- 

 lian results, if we assume that the hereditary characters are distributed among 

 dift'erent chromosomes. A point of great interest is what interaction, if any, 

 takes place between the chromosomes during conjugation, but for an answer to this 

 question only the indirect evidence of heredity is available. There is another 

 difficulty : if unit characters are sorted out by means of the separation of whole 

 chromosomes, then, in such a form as that of Ascaris, with only two chromosomes 

 in its somatic cells, mixing of characters would be impossible, except in the indi- 

 vidual concerned, for maternal and paternal characters would be completely 

 separated during reduction ; also, in such forms as Canna, which have only a 

 small number of chromosomes, there should be an extraordinarily high degree of 

 correlation in the sorting of the unit characters. 



The process of fertilisation, though sharply characterised in its higher mani- 

 festations, seems almost incapable of exact definition either physiologically or 

 morphologically, for such reduced conditions as ' apogamy ' and ' parthenogenesis ' 

 link it on to vegetative reproduction. Nuclear fusions and reductions appear to 

 occur in plants apart from reproduction, and in some graft-hybrids there is 

 eviden'^e that the fusing of vegetative cells has led to the mixing of characters 



2. The Protozoan Life-Cycle. By G. N. Calkins.— See p. 596. 



3. The Maturation of Parthenogenetic Eggs. By L. Doncaster, AI.A. 



The first systematic work on the maturation of parthenogenetic ogas was that 

 of Weismann and Ischikawa (1888). In a number of Entomostraca and Rotifers 

 they found that parthenogenetic eggs produce one polar body, fertilisable eggs 

 two, and they regarded this as being probably a general rule. It was soon dis- 

 covered, however, that eggs which produce two polar bodies may develop partheno- 

 genetically. Plattner (1888) found this in the moth Liparis dispar, the eggs of 

 which may develop although not fertilised; and Blochmann (1889) showed that 

 two maturation divisions take place in the Bee's egg, whether fertilised or not. 

 This has been confirmed by Petrunkewitsch (1901). In these cases the egg may 

 be fertilised, but develops whether spermatozoa are present or not. Henking 

 (1902) found that in the gall-fly Rhodites there are two maturation divisions, and 

 in this case the agg is rarely if ever fertilised, males being extremely rare. Since 

 then the same thing has been found in Sawflies, in which there are always two 

 maturation divisions ; and in some species virgin eggs yield males, in others 

 females ; in some of the latter males are unknown. Henking believed that in 

 Mhodites there was no reduction in Weismann's sense, and the same is probably 

 true at least of the female-producing Sawflies ; but according to Petrunkewitsch 

 the chromosome number is reduced in the Bee, and when the egg is not fertilised 

 it is automatically restored to the somatic number. Very little is as yet known 

 on this subject ; it is almost certain that when there is only one maturation 



3c2 



