No. 460.] STUDIES ON PLANT CELL. V. 229 



in animals. Probably the most important feature of fertilization 

 is the close union of the gamete nuclei through which the 

 chromosomes of both enter into the first mitotic Fgure of the 

 new generation. It involves the organization of the first cleav- 

 age spindle, which inaugurates the new generation, and the his- 

 tory of the paternal and maternal chromosomes of the gametes 

 at this time when the number becomes doubled. 



Several zoological papers have developed in the past few years 

 some very important conclusions concerning the individuality of 

 the paternal and maternal chromosomes, as maintained during 

 the fusion of the gamete nuclei and in the formation of the first 

 cleavage spindle. It has been generally believed for some time 

 see general review in Wilson (: oo, p. 204) that the fusion 

 of gamete nuclei did not involve a coalescence of the chromo- 

 somes but that both paternal and maternal chromosomes main- 

 tained complete independence of one another and that all entered 

 into the first cleavage spindle as structures quite as distinct as 

 when formed during spermatogenesis and oogenesis. Hacker 

 and Riickert have shown for Cyclops that the gamete nuclei 

 divide side by side in the first mitosis following fertilization, and 

 Hacker followed these double nuclei as far as the i6-celled stage 

 when they were still distinct from one another. A few notable 

 investigations of recent years have identified chromosomes accu- 

 rately as maternal and paternal not only in the first cleavage 

 spindle but through certain succeeding mitoses and finally at 

 the period of gametogenesis when sperm and egg were again 

 formed. The above principles have been established chiefly 

 through a series of papers of Montgomery, the chief being a 

 lengthy investigation of 1901, and contributions of Sutton 

 (:O2; 103) and Moenkhaus (:O4). They have given us clear 

 evidence that the chromosomes not only maintain their com- 

 plete individuality throughout successive generations but are 

 distributed with gametogenesis and fertilization in various pos- 

 sible combinations that can be expressed by mathematical for- 

 mulae furnishing the basis for certain ratios that approximate 

 the teachings of Mendel's law. We shall have occasion to refer 

 to these in Section V when the subjects of gametogenesis, reduc- 

 tion of chromosomes, and hybridization will be discussed. 



