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 figure 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 zoólogical 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 (: 00, p. 204) — that the fusion 
of gamete nuclei did not involve a coalescence öf 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 oógenesis. Hacker 
and Rückert have shown for Cyclops that the gamete nuclei 
divide side by side in the first mitosis following fertilization, and 
Häcker followed these double nuclei as far as the 16-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 
(102; :03) and Moenkhaus (:04). 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- 
mula 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. - 
