1042 The American Naturalist. ` [December, 
EMBRYOLOGY.’ 
Entwicklungsmechanisches.—A waiting the publication in the 
Zeit. f. Wiss. Zool. of a fully illustrated account of his exceedingly 
important work upon the value of cells in cleaving eggs, Hans Driesch? 
puts forth a short preliminary notice of results recently obtained at 
Naples. 
Having previously shown’ that one of the first two cleavage cells in 
an echinoderm could, by itself, form a complete larva, the author now 
wishes to combat the view that any real process of regeneration here 
leads to the formation of the symmetrical whole animal from the half 
ovum. This idea of a regenerative process has just been maintained 
by Chun in a paper presented to the Deutsche Zool. Gesellschaft, and 
very briefly noticed in the Zool. Anz., xv, June, 1892, p. 225. Chun 
separated the first two cleavage cells of the Ctenophore Bolina, and 
found each could produce a half-animal that later became a complete 
one by regeneration. This process was seen also in many eggs not 
artificially interfered with. . 
ans Driesch removes one of the first four cleavage cells of a sea- 
urchin and finds the remaining three cleave as if the fourth were 
still present, yet later a normal, but smaller, blastula (and in more 
than twenty cases a normal pluteus) is formed. One of the four cells 
may also, in some cases, give rise to a normal but very small pluteus. 
Thus we may take almost any fraction of the cleavage material and, 
if it is not too small, obtain an animal differing from the normal only 
in size. 
The author maintains that there is no reformation of the removed 
cleavage material, but the amount present closes in to form 4 small 
. blastula. There is no regeneration. 
In these facts is also seen the fundamental identity of the cleavage 
cells, their lack of preordination. To emphasize this conception 
the value of cleavage cells the author communicates the results of 
experiments the details of which we hope will soon be made known m 
his complete demonstration. In the egg of the sea-urchin the first 
three spindles lie in an equatorial plane, then the next four in & verti- | 
1This department is edited by Dr. E. A. Andrews, Baltimore, Md. 
?Anatomischer Anzeiger, vii, Aug., 1892. ` 
*See AMERICAN NATURALIST, Feb., 1892, p. 178. 
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