152 Transactions of the Society. 



the fertilized ova produce females. An interesting accessory dis- 

 covery is that in Phylloxera and Aphides; the males have in their 

 bodies one chromosome fewer than the, females have. " The male- 

 producing egg," Wilson notes, " must therefore eliminate one 

 chromosome, and this, we cannot doubt, is the X-element." 



25. These cytological studies are so very striking that one 

 inquires anxiously as to the distribution of the phenomena in the 

 animal kingdom. There have been some noteworthy recent exten- 

 sions. 



An accessory chromosome is reported by Boveri and Gulick in 

 Hcterakis, a Nematode of the pheasant. The ovum has live 

 chromosomes ; the sperms are of two types, one with four, the 

 other with five — a condition similar to that described by Wilson 

 for Protenor, one of the Hemiptera. In the common Ascaris 

 mcgaloccphala there is also evidence of an accessory chromosome, 

 but it seems at present somewhat discrepant and difficult. As 

 one would expect from the difficulty of the inquiry, there is still 

 considerable discrepancy of description in regard to many cases in 

 which an accessory chromosome has been affirmed. It is very 

 interesting to inquire whether there is any hint of an accessory 

 chromosome in Vertebrates. In a recent paper, Professor M. F. 

 Guyer brings forward evidence to show that in man half of the 

 spermatids (or immature spermatozoa) have ten, and half twelve 

 chromosomes, which would correspond to one of Wilson's cases, 

 Syromastcs, where half of the spermatids were found to possess 

 two more chromosomes than the others. Guyer has found evidence, 

 still unpublished, which leads him to think that, as regards acces- 

 sory chromosomes, conditions obtain among Vertebrates (fowl, 

 guinea-pig, rat, and man) similar to those found in numerous 

 Tracheates, and he ventures to express the expectation that the 

 somatic cells of man will be found to contain twenty-two chromo- 

 somes, and those of woman twenty-four chromosomes. 



26. The theory that the presence of one X-element in a fer- 

 tilized ovum means male offspring, and that the presence of two 

 means female offspring is morphological, and our physiological 

 sense is left unsatisfied. Is the difference significant in itself, or 

 as an index of metabolic differences ? If the eggs with more 

 chromatin than their neighbours develop into females, and if 

 chromatin be an index of a relatively preponderant anabolism or 

 anabolic capacity, can the theory be brought into line with the 

 thesis of " The Evolution of Sex," that the female is the outcome 

 and expression of relatively preponderant anabolism, and the male 

 of relatively preponderant katabolism ? On the other hand, it 

 may be that the additional chromatin material is of qualitative 

 importance. To give point to his theory, Professor E. B. Wilson 

 suggests quite provisionally that the X-element contains factors 

 (enzymes or hormones ? ) that are necessary for the production of 



