158 The American Naturalist. [February, 
EMBRYOLOGY.’ 
Experimental Embryology.—Under this title may be included 
two most interesting recent contributions to our knowledge of the sig- 
nificance of the cleavage phenomena in animal eggs. Both deal with 
. the cleavage phenomena of eggs influenced by experimental interfer- 
ence; the one in the case of a Vertebrate, the other in an Echino- 
derm. 
Prof. E. B. Wilson,’ of Columbia College, finds that the cleavage 
cells of an Amphioxus egg when shaken apart are yet capable of 
developing into gastrulas or even into complete larve of perfectly 
normal structure. Yet the size of the gastrule or larve is determined 
by the size of the cleaving cell; thus if one of the first two cells is 
taken the resulting gastrula is half the normal size, if one of the first 
four is taken, the gastrula is one-fourth the normal bulk. Gastrulas 
of one-eighth the normal size occurred but were not products of isolated 
cells in the eight-cell stage; in fact, the experiments go to show that 
one of these first eight cells is incapable of forming a gastrula. There 
is thus an early limit set upon the potentialities of the cleavage cells. 
This, moreover, seems to be a qualitative and not a quantitative limit. 
The homogeneous, undifferentiated character of the cells is lost at the 
eight-celled stage. 
When the cells are incompletely separated, double, triple, and even 
quadruple embryos are formed. 
Comparing the development of the isolated cells of Amphioxus with 
what is known of similar phenomena in-other Vertebrates as known 
from the work of Roux upon the frog, or with the facts established for 
Echinoderms by Dreisch and others, we find an important and fun 
mental difference in the time at which individuation and symmetry be 
come apparent. While in the Echinoderm the partial development pro- 
ceeds at first as if all the cells were present, and only later what maf, 
improperly, be called a p fregeneration, forms that which waslack = 
ing to the completion of a normal symmetrical embryo, in Amphioxus = 
as the author shows by di ivi te ol tions than 
had hitherto been made upon the exact mode of cleaving,—“the isolated 
bss department is edited by Dr. E. A. Andrews, Johns Hopkins Unr 
"On Multiple and Partial ioxus. Anat. Anz, IAA i 
Nos. 23-24. Pp. ; ial Development in Amphioxus. Ana , a 
