288 The American Naturalist. [March, 
tiple fertilization is concerned or that subsequent events are the cause. 
The cause of double monsters lies in some abnormal state of the ova- 
rianegg. This state of the egg may be like that that has in recent 
experiments produced double formations from half eggs; that is, the 
abnormality may be its division into more or less separate halves, each 
of which would form a complete individual if separated from the 
other. 
Double individuals are thus to be regarded as coming from imper- 
fectly divided ovarian cells ; eggs similar to the somatic cells that are 
found with two nuclei. A complete division of the germ material pro- 
duces separate individuals, a very slight division, double monsters ; 
between these extremes are identical twins. 
The formation of double monsters would be, in this speculation, a 
process of arrested development! 
Fusion of Blastomeres.—Dr. Arnold Graf‘ briefly describes a 
remarkable case of retrogressive cleavage in the eggs of the sea-urchin 
Arbacia. 
Some eggs compressed under a cover-glass after the method of 
Driesch, divided into flat plates of 16 cells that quickly passed into 
32 (here some abnormal conditions may be suspected). When the 
pressure was removed by adding more water, the cells began to fuse so 
that their number became reduced to 15 and then 14! At first each 
has two or three nuclei according as it is made by the fusion of two or 
of three cells, but later the nuclei fuse and the cells change their posi- 
tions and shapes. The same phenomenon was seen ina plate of 8 
cells. 
It is claimed that only those cells unite that are closely related: the 
daughter cells of one mother cell fuse together. 
Unfortunately nothing is known of the possible future of such em- 
bryos nor of the effective causes at work in producing them, and so 
this notice serves more as a stimulus to work than as a contribution to 
our knowledge of the mechanics of embryology. - 
Temperature and Development.—Professor O. Schultze’ finds 
that the eggs of Rana fusca may be kept in water at 0° C for 14 days 
when in the gastrula stage without losing the power to form normal 
embryos. During this period there is a complete cessation of develop- 
ment. 
‘Zool. Anz., XVII, Dec., 1894. 
5 Anat. Anz., X, Dec. 19, 1894. 
