450 Beard and Murray. — Reproduction in Animals 
united action of two processes, (i) It is initiated before the 
maturation, perhaps at a very early period, by the sup- 
pression of a transverse division of the chromatin loop, in 
consequence of which the chromosomes remain attached in 
pairs or couples. (2) It is accomplished in the second division 
of the ripening by the passage of the chromosomes of each 
pair to opposite poles \ He goes on to say that the first 
process alone leads only to a pseudo-reduction, the true 
number of chromosomes persisting, being only masked, and 
therefore capable of reappearing. The process, however, 
appears necessary in order that the subsequent reduction 
should be effected. A theoretical explanation of this has 
been attempted above. 
It may at this juncture be useful to consider what must 
have been the general result of the initiation of conjugation 
between unicellular organisms in past ages. When conju- 
gation between pairs of similar cells arose among the primeval 
Protozoa (or Protophyta) the original form of this process 
was bound to result in the ‘ creation ■’ of two different 
generations. These were characterized primarily by a dif- 
ference in the number of chromosomes. The one generation 
with double chromosomes was itself never capable of conju- 
gation, it could only give rise to new forms by fission, and it, 
or its progeny so produced, could only bring about a new 
conjugation by first producing (spore-formation) a generation 
in which the number of chromosomes was reduced in each 
individual product to the original one, which obtained ante- 
cedent to a conjugation. 
1 It is worthy of notice that Farmer has recently stated the following facts 
concerning the reduction in plants : — Two features characterise the karyokinesis 
of the spore mother-cell in Hepaticae. The first of these is that the number of 
chromosomes is reduced to one half as compared with antecedent mitoses in the 
sporophyte, and this reduced number is apparently retained in the gametophyte. 
The second point is that the spore-forming mitoses are what Fleming has termed 
* heterotypic ’ in character. (J. B. Farmer, Spore-formation and Karyokinesis in 
Hepaticae. Annals of Botany, Vol. ix, June, 1895, pp. 363-364.) These facts 
appear to agree absolutely with what Ruckert found in Copepods, but of course in 
the one case (animals) the reduction occurs at the ‘ripening’ of the sexn' 
products, in the other (plants) at the spore-formation. 
