196 Lloyd Williams. — Studies in the Dictyotaceae. 
four-celled. In material which was left for nine hours after the addition 
of antherozoids the following stages were found : 
(1) Nuclei with two nucleoli andspirem. 
(2) Nuclei with two nucleoli and chromatin segments. 
(3) Spindles. 
(4) Diasters. 
(5) A few binucleate stages. 
In addition to these, however, there was a large number of eggs 
which had been liberated from half an hour to an hour before the addition 
of antherozoids, and so had become ‘ stale ’ and incapable of being fertilized ; 
these showed various stages of parthenogenesis. 
V. The Parthenogenesis of Unfertilized Eggs. 
A very large number of germination experiments was carried out 
upon the oospheres of Dictyota . Most frequently antherozoids were added, 
but control experiments were also performed with the antherozoids omitted. 
In all the former cases there was a mixture of germlings which had 
followed the normal course of segmentation as detailed in the preceding 
section, together with others which showed the characteristic phenomena 
of parthenogenesis described below. There is no difficulty in distinguish- 
ing between the two sets of figures. Those of the fertilized eggs can 
easily be recognized by their resemblance to ordinary karyokinetic figures ; 
those of the parthenogenesis are quite abnormal in appearance. That 
the latter really are parthenogenetic figures is confirmed by the fact that 
they are very numerous in the control cultures, to which no sperms were 
added, and that these never show any signs of normal mitotic figures. 
Similar irregular multipolar figures are obtained in certain animal 
eggs, chiefly as the result of artificial stimulation or of polyspermy, and 
also in malignant tumours. The cases described by Loeb, Morgan, the 
Hertwigs, Wilson, Galeotti, and a great many others are too well known 
to need recapitulation. It is important, however, to bear in mind that 
parthenogenesis in Dictyota is not the result of any such unusual conditions ; 
the very fact that they occur side by side with perfectly normal karyo- 
kinetic figures is sufficient to exclude any such supposition. 
As it is very important to ascertain the exact number of chromo- 
somes in the figures, and to know whether two nucleoli are present or 
only one, it is evidently essential to compare together all the sections 
of a nucleus before drawing any conclusions. I have throughout adhered 
rigidly to this practice, but in dealing with cultures of oospores and 
tetraspores there are certain difficulties which do not confront one when 
sectioning the reproductive cells on the plant itself. It is very difficult 
to get cultures of Dictyota eggs free from sand, diatoms, &c., as in 
