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Prof. E. B. Wilson. 



development, and that they are qualitatively different in respect to their 

 individual influence. Eggs into which two spermatozoa are caused to enter 

 develop into larvse that are almost always pathological, deformed or monstrous. 

 The first cleavage of such eggs is by a tripolar or quadripolar division, 

 and the cytological examination proves that this involves initial and 

 apparently irreversible aberrations in the distribution of the chromosomes 

 to the embryonic cells. Boveri's analysis, carried out with characteristic 

 sagacity and thoroughness, seems to leave no escape from the conclusion 

 that the abnormal combinations of the chromosomes thus produced are 

 the cause, and the only cause, of the abnormal forms of development. 

 The chromosomes must therefore be qualitatively different. This conclusion 

 has been confirmed and rendered more specific by many later researches. 

 It was proved, for instance, that in certain animals one of the chromosomes, 

 or a small corresponding group of chromosomes, stands in some special 

 relation to the determination of sex and the heredity of sex-linked 

 characters. The study of hybrid sea-urchin larvae by Baltzer, Herbst, and 

 others, gives strong reason to conclude that many of the aberrations which 

 they show in respect to the combination of maternal and paternal 

 characters result from corresponding aberrations in the distribution of 

 maternal and paternal chromosomes. In the evening primroses, the 

 researches of Lutz and of Gates have shown that the gigas type of mutant 

 has arisen in association with a doubling of all the chromosomes ; recently 

 the same observers show that the lata type is characterised by, and 

 probably has arisen through, the presence of a single extra chromosome. 

 To the still more recent important results of Gregory on the Chinese primrose 

 I will presently refer. 



The conclusion of Montgomery was not less important, but failed at first 

 to receive the consideration that it deserved. Among the suggestions that 

 immediately followed upon Weismann's speculations concerning the reduc- 

 tion division, one of the most fruitful was that of Henking (1891), that the 

 reduction of the number of chromosomes in the germ-cells is initiated by 

 their conjugation two by two in pairs during synapsis, to be followed by their 

 disjunction in the reduction division. Montgomery drew the bold conclusion 

 that in this process each chromosome of paternal descent unites with a 

 corresponding or homologous one of maternal descent ; and he suggested that 

 this process, though occurring at the very end of development, might be 

 regarded as the final step in the fertilisation of the egg. This surprising 

 conclusion was based on a comparative study of the size-relations of the 

 chromosomes in the diploid and haploid nuclei. I well remember the 

 scepticism with which I, like many others, first received it. The conjugation 



