804 STUDIES IN GENERAL PHYSIOLOGY 
active movements in the blastula and gastrula stage. These 
latter isolated embryos continued their development nor- 
mally. In this way either separate or “Siamese” twins were 
formed from a single egg. It often happened that a repeated 
outflow of the protoplasm occurred, and then three or even 
a larger number of joined proto- 
plasmic drops were formed from 
one egg. In a number of cases, 
which was by no means small, I 
obtained, in consequence, joined 
triplets or quadruplets." I suspect, 
however, that in the gastrula stage 
many of these multiple embryos are separated from each 
other through the active movements of the egg, as triplets 
are relatively rare in the pluteus stage. On the other hand, 
it was a simple matter to obtain double plutei in large num- 
bers. All these double and triple plutei lived as long (about 
two weeks), and were as well and as complete in their form, 
as the plutei produced from a normal egg. 
2. As has already been mentioned, the eggs were intro- 
duced into the diluted sea-water before the beginning of 
cleavage, and as only one nucleus was present at this time, 
only one of the two drops of protoplasm contained a nucleus. 
Nevertheless, both drops developed into a complete embryo. 
How did the drop of protoplasm which was at first without 
a nucleus obtain a nucleus? This happened in a very simple 
way in the course of cleavage. Cleavage did not take place 
in the sea-water which had been diluted 100 per cent., but 
as soon as the eggs were returned to the normal sea-water, 
cleavage began. The first line of cleavage was perpendicu- 
lar to the common diameter of both spheres (Fig. 70). The 
FIG. 69 
1These facts have been questioned by one author on the basis of inadequate 
and imperfect experiments made by him. During my experiments on artificial 
parthogenesis I have had a chance to verify amply the statements made in this 
paper. 
Digitized by Microsoft® 
