678 STUDIES IN GENERAL PHYSIOLOGY 
The fact that the fusion of two eggs into one giant embryo 
occurs so much more readily in Cheetopterus than in Arbacia 
may be due to the difference in the viscosity of the two eggs, 
The formation of one giant embryo from two eggs in 
Cheetopterus is so very interesting for the reason that the 
Cheetopterus egg possesses a characteristic cell-lineage. We 
must conclude from this that the cell-lineage is either a sec- 
ondary element in the formation of the embryo or that the 
earlier processes of differentiation in the Chetopterus egg 
are partly or wholly reversible (see section x). 
I have made very few experiments with CaCl,, but in 
these giant embryos were formed. Eggs that had been in a 
solution of 90 c.c. sea-water + 10 c.c. 5n CaCl, for one hour 
gave rise to a number of giant embryos. A sure way to 
produce giant embryos in Cheetopterus is to put the unfertil- 
ized eggs for about one hour into a mixture of 97 c.c. sea- 
water +3 c.c. 24n KCL 
I have occasionally, but very rarely, found that the fertil- 
ized eggs of Cheetopterus show agglutination in normal sea- 
water. The same phenomenon seems to occur in the eggs of 
Ascaris, according to Zur Strassen.! 
Dwarf embryos are rarely found in Chetopterus. I have 
found them in the experiments with HCl. Perhaps the 
existence of a membrane prevents the unfertilized eggs of 
Cheetopterus from forming dwarf embryos as easily as the 
unfertilized eggs of the sea-urchins. 
VII. ON DIFFERENCES BETWEEN THE ARTIFICIAL PARTHENO- 
GENESIS OF ECHINODERMS AND CHETOPTERUS AND THE 
POSSIBILITY OF A HYBRIDIZATION BETWEEN THE TWO 
It is impossible to hybridize Arbacia and Cheetopterus in 
normal sea-water. I have tried a number of experiments 
with negative results, as was to be expected. The negative 
1ZuR STRASSEN, loc. cit. 
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