SUMMARY OF CURRENT RESEARCHES 



RELATING TO 



ZOOLOGY AND BOTANY 



(PRINCIPALLY INVERTEBRATA AND CRYPTOGAMIA), 



MICROSCOPY, Etc.* 



ZOOLOGY. 



VEETEBRATA. 

 a. Embryologry.t 



Accessory Chromosomes in Man.}— M. F. Guyer describes the two 

 accessory chromosomes as found in man, with other features of human 

 spermatogenesis. Twenty-two chromosomes, differing considerably in 

 size, were found to occur in all spermatogonia in which the investigator 

 was able to make a definite count. Iu a few instances, two — apparently 

 the two accessory chromosomes — were seen considerably to one side of 

 the main mass of chromosomes, surrounded by a small clear court of 

 cytoplasm. Twelve chromosomes appear for division in the primary 

 spermatocyte, of which ten are evidently bivalent and two accessories. 

 The two accessory chromosomes pass undivided to one pole of the spindle 

 considerably in advance of the other chromosomes, with the result that 

 half of the daughter-cells in this division receive twelve, and half only 

 ten univalent chromosomes. This is evidently the reduction division. 

 The ten univalent chromosomes which passed to the one secondary 

 spermatocyte unite again in pairs — at least, in the majority of cases — 

 to form five bivalent chromosomes, which appear at the equator of the 

 spindle when the cell is ready for division. The division here is 

 presumably an equation and not a second reduction division, judging 

 from the size, shape and general appearance of the resulting daughter- 

 chromosomes. Thus, while each of the spermatids formed as a result of 

 this division receives only five chromosomes, the latter are bivalent, and 

 equivalent to ten of the somatic or spermatogonial chromosomes. There 

 is some slight evidence that the secondary spermatocytes may occasionally 

 divide with their chromosomes in their original condition of univalence. 

 Ten of the twelve chromosomes which passed to the other pole of the 

 spindle in the primary spermatocyte behave in the way just described. 



* The Society are not intended to be denoted by the editorial " we," and they 

 do not hold themselves responsible for the views of the authors of the papers 

 noted, nor for any claini to novelty or otherwise made by them. The object of 

 this part of the Journal is to present a summary of the papers as actually pub- 

 lished, and to describe and illustrate Instruments, Apparatus, etc., which are 

 either new or have not been previously described in this country. 



t This section includes not only papers relating to Embryology properly so 

 called, but also those dealing with Evolution, Development, Reproduction, and 

 allied subjects. \ Biol. Bull., six. (1910) pp. 219-34 (1 pi.). 



