B. F. Kingsbury 123 



spermatogenesis should be attempted is that of mitosis. The two " re- 

 ducing " divisions are mitoses with certain peculiarities and should be 

 considered simply as such and investigated from that standpoint. Any 

 explanation of oogenesis or spermatogenesis must be first of all an 

 explanation of cell-divisions. I do not mean that this has not been 

 done by many workers on spermatogenesis; and full appreciation is felt 

 of the excellence of the work of those employing spermatogenesis divi- 

 sions for the investigation of mitosis. Flemming's classical paper in 

 1887, with its recognition of the divergent types of mitosis, uninfluenced 

 as it was by theoretical interpretations, seems to me to represent a much 

 more healthy attitude than do many of the later contributions. Occa- 

 sionally the influence of theory has been responsible for evident eri'ors 

 of interpretation, as, in Amphibia, vom Rath's work on the spermato- 

 genesis of Salamandra. 



As is well known, in several groups, by repeated and confirmatory 

 investigations, the absence of " reducing ". divisions has been shown, and 

 this is especially evident in Amphibia, Ascaris, and Lilium. In Am- 

 phibia, Flemming, Meves, McGregor, Cai-noy et Le Brun, Eisen and 

 myself have furnished strong demonstration, Ascaris megalocephala 

 has been tested by Boveri, Brauer and Hertwig. Among plants, small 

 doubt may be felt about the divisions in the Liliacece from the work of 

 Strassburger, Guignard, Mottier, Sargent and Dixon. A single well- 

 authenticated case of the absence of transverse divisions seems to me 

 to be fatal to the theory of a qualitative reduction, and warrants its 

 rejection as a working hypothesis. In its abstract form, it is a theory 

 that cannot be disproved, although as reconstructed it cannot offer a 

 more suitable basis for interpretation. While in certain forms both 

 divisions of the spermatocyte have been shown to be longitudinal," in 

 other groups I think it may be considered fairly well proved, that one 

 of the divisions is as certainly transverse. Carnoy and Le Bruri, it seems 

 to me, go too far in doubting correctness of observation in the finding 

 of transverse divisions. In Insects and Copepods, certainly, the con- 

 cordance of results permits but one interpretation — that one of the 

 divisions is transverse. Both conditions must be harmonized, then, in 

 any theory of spermatogenesis, and this the Weismann theory does 

 not do. 



If we view the divisions of the spermatocyte from the standpoint of 



5 In a recent paper by King on the oogenesis of Bufo, tlie conclusion reached is that 

 there both divisions are equation divisions, the "splitting" in the first maturation 

 division taking place very early. 



