ARTIFICIAL PrRopuctTion oF NorMAL Larv& 583 
19n CaCl, with 10 c.c. of distilled water I occasionally saw 
an egg in the two-cell stage. In more dilute CaCl, 
solutions no trace of a segmentation occurred. Hence Mg 
and K were more favorable than Na and Ca ions for the con- 
centration used in the experiments. It is very evident from 
these experiments that the optimum concentration for each 
of these four chlorides is different. 
In a £n LiCl solution the majority of eggs remained un- 
segmented, and only very few reached the two-cell stage. 
Mixtures of LiCl with sugar were no more advantageous. 
In pure glycerin and sugar solutions of the same osmotic 
pressure as that of a $n NaCl solution no egg segmented. 
It is evident that the quality of the ions is of more impor- 
tance in these experiments than the osmotic pressure, and 
that NaCl is not an indifferent substance. 
Two chlorides in solution.—In a solution of one chloride 
the eggs of Arbacia cannot reach the blastula stage. Are 
mixtures of two chlorides more favorable for segmentation? 
Among the possible mixtures of the two chloride solutions 
of the same osmotic pressure as the sea-water I found those 
between 19n MgCl, and 12 CaCl, the most favorable. 
The following twelve mixtures were prepared: ' 
(1) 100 cc. 422 MgCl.+ Occ. 4°” CaCl, 
(2) aa “ 
(3) 90 «“ 4+ 10 «“ 
(4) 80 «“ + 20 “ 
(5) 70 “ + 30 “ 
(6) 60 “ + 40 «“ 
(7) «BO “ + 50 “ 
(8) 40 ‘ + 60 “ 
(9) 80 «“ oe (01 “ 
10) 20 “ + 80 «“ 
(11) ~—- 10 . + 90 “ 
(12) 0 «“ +100 «“ 
1It will save repeating these figures if I may state here that the same twelve 
proportions were used in all the following experiments with two chlorides in 
solution. 
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