66 THE AMERICAN NATURALIST. (Vor. XXXIX. 
not only by people unacquainted with the facts won by science 
and with the methods of scientific research, as bee-keepers for 
instance, but also by men of very considerable scientific educa- 
tion, especially physiologists. It seems to me therefore season- 
able to review briefly these objections, in order to determine 
what, if anything, has been gained through this controversy, 
so that we may know how the question of parthenogenesis now 
‘stands. 
Our knowledge of fertilization and parthenogenesis, acquired 
in the study of many different animals, may be recapitulated in 
the following words : 
1. Both the egg ready for fertilization and the mature sperm 
show a reduction in the number of chromosomes of their nuclei 
to one half of that found in somatic cells. ; 
2. No matter how many spermatozoa succeed in entering the 
egg, the nucleus of only one of them, under normal conditions, 
fuses with the egg-nucleus, thus restoring the chromosomes to 
their original number. All other spermatozoa are absorbed. 
3. The centrosome of the egg disappears after the second 
polar cell is formed, its functions being assumed by the centro- 
some of the spermatozoön. 
4. In most parthenogenetic eggs no reduction of chromo- 
somes takes place — only one polar cell being formed — and the 
€8g-centrosome remains active. | 
Now, all of the objections alluded to above are directed against 
one or more of these four propositions. As, however, it is in 
these propositions that our present understanding of partheno- 
genesis is epitomized it is of urgent importance to discover how 
much of truth these objections contain. 
First of all I shall consider the objections brought forward by 
the physiologist Bethe and the zoölogist Bresslau. Both claim 
to find the essence of fertilization not in the union of the sperm- 
nucleus with the egg-nucleus, but in the entrance of spermatozoa 
into the egg. Bethe (:04) says explicitly: “I consider an egg 
fertilized when a spermatozoón has entered it. What becomes 
of this spermatozoön later on is another question.” He says, 
further, that not alone the chromosomes of the nucleus enter 
the egg, but also other substances, of whose fate we know 
