590 The American Naturalist. [July, 
The larve, when killed and examined, are found to have 
abnormally small nuclei, which is accounted for by the suppo- 
sition that the single male nucleus of the sperm does not fur- 
nish as much material as the male and female nuclei normally 
do when combined. 
If we accept these statements we have, indeed, most conclu- 
sive proof that in a male nucleus the sperm may transfer toa 
new organism the qualities of its parent. 
The difficulties of the experiment lie in the unfavorable 
nature of the hybridization, only one in a thousand eggs being 
fertilized, so that of 200 actually isolated none happened to 
develop ; then again the various abnormalities, half embryos 
and dwarfs that we may assume occur, make it a difficult ques- 
tion, we think, to decide as to the specific characters of the 
larvee being due to inheritance or accidental resemblance from 
imperfect development. 
The recent work of Driesch’ is the last contribution in exper- 
imental embryology that has come to our notice. To deter- 
mine the effect of light upon cleaving eggs he exposed the 
eggs of Echinus microtuberculatus, Planorbis carinatus and Rana 
esculenta to daylight and to complete darkness as well as to 
variously colored light. The result was that not only cleavage 
but also the formation of organs took place quite normally in 
time and form, entirely irrespective of the presence or charac- 
ter of light. 
The more noticeable and unexpected part of the paper, how- 
ever, deals with the question of self differentiation, as illus- 
trated by experiments upon sea urchin eggs (as yet he has not 
succeeded in applying appropriate methods to eggs of frogs 
and Planorbis). 
The eggs of the sea urchin in the two celled stage are shaken 
vigorously for five minutes in a test tube (some may need 
repeated shaking), and then such isolated cells as are present 
are quickly picked out and examined under the microscope in 
separate dishes of sea water. 
1Hans Driesch. Entwicklungsmechanische Studien. I. Der Werth der beiden 
ersten Furchungs-zellen in der Echinodermenentwicklung. II. Uber die Beziehung 
des Lichtes zur ersten Etage der theirischen Formenbildung. Zeit. f. wiss. Zool., 
liii, 1891, pp. 160-183, plate 7. 
