VII 
THE FIRST EXPERIMENTS UPON THE OSMOTIC ACTIVA- 
TION OF THE UNFERTILIZED EGG OF THE 
SEA-URCHIN (Arbacia) 
1. As already mentioned, I began my investigations with 
the anticipation that it must be possible to induce the un- 
fertilized eggs to develop by treating them with bases or acids. 
For several weeks in the summer of 1899 I conducted experi- 
ments in this direction on the eggs of a sea-urchin, Arbacia, 
at Woods Hole, without obtaining any other result than that 
the unfertilized eggs of Arbacia placed in 100 c.c. of sea-water+ 
1 c.c. of N/i10 NaOH begin_to segment after remaining in the 
solution for about five hours. The cleavage, however, was very 
irregular and did not go beyond the early stages—two or four 
cells. At the same time the eggs showed a tendency to become 
amoeboid. The experiments with acids (HCl, HNO,, H.SO,) 
showed that no cleavage took place in acidified sea-water, but 
that a few divisions might be observed in unfertilized eggs if 
they were placed for about ten minutes in 100 c.c. of sea-water + 
2 or 3 c.c. of N/10 HCl and then replaced in normal sea-water.! 
Experiments with salt solutions which were isosmotic with 
sea-water gave no better results. When the summer of 1899 
had almost entirely elapsed in this manner without any 
success, I at last investigated the effects of hypertonic solutions. 
10/8 m (grammolecular) solutions of NaCl, KCl, CaCl,, and 
MgCl,, were prepared and mixed in different proportions 
with sea-water. After prolonged experiments I found that if 
unfertilized sea-urchin eggs were exposed for two hours to a 
mixture of 50 c.c. of sea-water+50 c.c. 10/8 m MgCl, and then 
i Loeb, ‘‘On the Artificial Production of Normal Larvae from the Unfertilized 
Eggs of the Sea-Urchin,’’ Am. Jour. Physiol., III, 434, 1900; Untersuchungen 
zur kiinstlichen Parthenogenese, p. 77, 1906. 
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