170 
W. Neilson Jones. 
male nucleus and one polar nucleus, instead of forming an exactly 
balanced system, still possess an attraction for (or are attracted 
by) the second polar nucleus. The case is, in fact, almost the 
converse of that in which the egg-cell is fertilized hy two sperma- 
tozoids. As a result of the triple fusion there is produced not a 
stable organism but a growth comparable to those resulting from 
parasitism—a growth which forms the endosperm. 
One may draw attention here to certain important and 
surprising results that have been obtained in the course of 
experiments with sea-urchins’ eggs. It has been found that unfer¬ 
tilized eggs can be “ fertilized,” or at least their development 
initiated, by purely chemical means—by immersing the eggs in 
solutions of certain salts. In some cases development has been 
brought about even by the mechanical operation of pricking the 
egg-cell with a needle. The egg-cell is not, therefore, dependent for 
development on the spermatozoid qua spermatozoid, but merely 
on the stimulus that is imparted to it by the entry of the latter. 
The stimulus to cell division imparted to the egg-cell by entry 
of the spermatozoid is thus in its results not unlike that imparted 
to the embryo of certain plants, such as the orchids, by infection 
of the seedling with the mycorhizal fungus. In neither case does 
cell division occur until the stimulus resulting from the presence of 
the missing member of the dual alliance is provided : as soon as this 
is applied normal growth proceeds. In the case of the egg-cell the 
normal stimulus can be imitated, in rare cases, by other and artificial 
means: an appropriate artificial stimulant has not been discovered 
yet for those curious cases in which there is arrested development 
of the seedling pending infection by the mycorhizal fungus. This 
difference of behaviour is probably more apparent than real, for it 
would seem relatively more simple to cause an orchid embryo 
to commence growth by substituting direct chemical stimulus 
for fungal infection, than to initiate development of an unfertilized 
egg-cell by the substitution of an artificial stimulus for that 
which results normally from fertilization by a male gamete . 1 
1 Some work of Calkins upon Paramecium is of interest in this connection 
as illustrating the use of an artificial stimulant in place of the one naturally 
occurring in a case of arrested development (“ Studies in the Life History 
of Protozoa IV.” Jour, of Exper. Zool. Vol. I., 1904). Maupas had shown 
that in Paramcecium the vigour and rate of vegetative reproduction gradually 
decreased in cultures, but was regained as the result of conjugation between 
two individuals. If this conjugation were prevented the individuals ceased to 
divide altogether and eventually died. Calkins found that the loss of vigour, 
which invariably occurred if conjugation were prevented, and led normally to 
a cessation of cell division and death, could be tided over and the race carried 
through further cycles of activity, by the use of artificial stimuli. By using 
extracts of beef, pancreas, etc., the race was carried on through four cycles 
of activity, i.e., past three depression stages. 
