CYTOLOGICAL STUDIES OF CENTRIFUGED EGGS 601 
divided, so that one of its products contains pigment, the other 
some oil, and at the same time the large cell has budded off a 
small cell rich in oil. It is important to note that the relative 
sizes of these blastomeres are the same as those of the normal egg, 
and that no variation in size takes place as a result of the different 
kinds of materials contained in them. 
I was anxious to isolate eggs in which all the yolk, plate l,fig. H, 
or oil, fig. G, was known to be present in a definite part of the egg; 
for it was conceivable at least that only those eggs develop nor- 
mally in which the induced segregation corresponds with certain 
polar relations of the egg. The normal distribution of yolk, oil 
and pigment makes such an interpretation highly improbable, 
nevertheless I wished to get definite information on this point. 
Therefore in the summers of 1907-8 I made more than 1000 isola- 
tions with no result; since the sets themselves from which these 
were taken went for the most part abnormally. At this time the 
season was almost past and even normal eggs isolated produced 
abnormal embryos. In 1909 I again returned to the question 
after I had found that centrifuged eggs from centrifuged females 
often produced normal embr^^os. Although not nearly so many 
eggs were isolated, in all combinations, I failed to get normal sets 
owing in part to the handling, and in part to the fact that even 
in good sets some eggs go abnormally. I soon gave up these 
laborious attempts to isolate single eggs; for, I found that in the 
living animal it was quite eas}^ to see in all stages up to the tro- 
chophore and even the veliger, the position of the pigment or of 
the oil. Sections of eggs up to and later than thegastrulation stage 
also showed that the yolk might be present in any part of the egg 
and normal gastrulation occur. I have examined hundreds of such 
sections but it did not seem necessary to give figures of them. 
A series of figures of the living trochophores and veligers 
are shown in plate 3, figs. I-XV. The pigment is red, the oil is 
bluish. It will be seen that these materials may lie in any part of 
the embryo without producing abnormal development ; figs. II-V; 
VII-XI; XIV-XV. It follows that none of the visible materials 
of the egg of Cumingia are essential to the development of special 
parts of the embryo. 
