4 CAPT. C. F. U. MEEK ON THE 



chromosomes. He found it in certain cases enclosed in a vesicle during, the 

 resting-stage, but considers this condition artificial and unimportaiit. 



Somewhat different results were obtained in 1905 by Montgomery working 

 upon Syrhula acidicornis, for he declared that the heterotropic chromosome 

 is represented in the spermatogonial cell by two chromosomes, and that it 

 divides at both maturation divisions. Robertson's researches however upon 

 the closely allied S. admirabilis afford no evidence of this paired condition, 

 and support the view that this chromosome passes entire to one pole at the 

 first maturation division, splitting longitudinally at the second : this seems to 

 be the normal occurrence in the Orthoptera, for it has been observed by 

 Baumgartner, Davis, Gerard, Gutherz, McClung, Nowlin, Otte, Robertson, 

 de Sinety, Sutton, Wilson, and others. 



The discovery in the male germ-cell of an odd chromosome, which passes 

 entire to one pole at a subsequent mitosis, and the discovery that in allied- 

 types the unequal members of one spermatogonial pair pass to opposite poles- 

 have proved that dimorphism of spermatozoa exists in certain groups : and, 

 since spermatozoa of the one kind produce males, and those of the other 

 females, sex, in these organisms, must be determined at the moment 

 when the spermatozoon enters the micropile, immediately prior to amphi- 

 mixis. This has given rise to the hypothesis that dimorphism of spermatozoa 

 occurs throughout the animal kingdom, and that sex is determined in this 

 manner. 



It is possible that the presence or absence of a particular chromosome is 

 the factor controlling sex ; but it is equally possible that this chromosome 

 contains only certain of the numerous characters peculiar to one sex, and 

 that its passage to one pole is closely connected with the passage to that pole , 

 of the ordinary chromosomes, after they have divided on the equatorial plate. 

 The function of the chromosomes is not yet understood : although the 

 majority of cytologists believe that the chromatin alone contains the bearers 

 of the hereditary characters, some still affirm that the cytoplasm is the sole 

 agent in this respect, and that the chromatin fulfils the subordinate role of a 

 nutritive substance. The experiments of Boveri upon the fertilization of, 

 enucleated Echinoderm ova appeared convincing, but unhappily the same 

 experiments repeated by Delage and others gave diametrically opposite 

 results. It seems of little importance whether the transmitted material is 

 composed of actual character factors, or whether it represents a con- 

 catenation of physical units, resulting in the phenomena implied in heredity ; 

 but it is important to ascertain by what means these phenomena are. 

 reproduced generation after generation. 



The character factors may eventually be found to reside in both chromatin 

 and cytoplasm, being distributed in the latter during the resting-stages for: 

 purposes of nutrition, and being collected together in the chromatin filaments- 

 only during the stages immediately preparatory to karyokinesis : this would 



