EARLY HISTORY OF THE GERM-NUCLEI 2?$ 



This surmise quickly became a certainty. Overton himself dis- 

 covered ('93) that the cells of the endosperm in the gymnosperm 

 Ceratozamia divide with the reduced number, namely eight ; and 

 Dixon observed the same fact in Firms at the same time. In the 

 following year Strasburger brought the matter to a definite conclusion 

 in the case of a fern (Osmunda), showing that all the cells of the 

 prothallium, from the original spore-mother-cell onwards to the for- 

 mation of the germ-cells, Jiave one-half the number of chromosomes 

 found in the asexual generation, namely twelve instead of twenty- 

 four ; in other words, the reduction takes place in the formation of 

 the spore from which the sexual generation arises, many cell-genera- 

 tions before the germ-cells are formed, indeed before the formation of 

 the body from which these cells arise. Similar facts were determined 

 by Farmer in Pallavicinia, one of the Hepaticae, where all of the 

 nuclei of the asexual generation (sporogonium) show eight chromo- 

 somes during division, those of the sexual generation (thallus) four. 

 It now seems highly probable that this will be found a general rule. 



The striking point in these, as in Hacker's observations, is that the 

 numerical reduction takes place so long before the fertilization for 

 which it is the obvious preparation. Speculating on the meaning of 

 this remarkable fact, Strasburger advances the hypothesis that the 

 reduced number is the ancestral number inherited from the ancestral 

 type. The normal, i.e. somatic, number arose through conjugation 

 by which the chromosomes of two germ-cells were brought together. 

 Strasburger does not hesitate to apply the same conception to ani- 

 mals, and suggests that the four cells arising by the division of the 

 oogonium (egg plus three polar bodies) represent the remains of a 

 separate generation, now a mere remnant included in the body in 

 somewhat the same manner that the rudimentary prothallium of angi- 

 osperms is included in the embryo-sac. This may seem a highly 

 improbable conclusion, but it must not be forgotten that so able a 

 zoologist as Whitman expressed a nearly related thought, as long ago 

 as 1878 : " I interpret the formation of polar globules as a relic of the 

 primitive mode of asexual reproduction.^ a Strasburger's view is 

 exactly the reverse of this in identifying the polar bodies as the 

 remains of a sexual generation ; and as Hacker has pointed out ('98, 

 p. 102), it is difficult to reconcile with the fact that true reduction 

 appears to occur already in the unicellular organisms (p. 277). The 

 hypothesis is nevertheless highly suggestive and one which suggests 

 a quite new point of view for the study not only of maturation but 

 also of the whole problem of sexuality. 



We may now return to the consideration of some details. In a 

 considerable number of forms, though not in all, the early prophase is 



1 '78, P . 262. 



