The InjluefTce of External Factors on Development 189 



hours old the blastoderms were raised up prominently on the yolks. 

 Many eggs died during early cleavage, and altogether the eggs are 

 decidedly abnormal. Neither of these salts acting alone would 

 give such an effect. When forty-two hours old the yolks are 

 shrunken and all of the embryos have a balloon-Hke pericardium 

 in front of the head, Fig. 12, pc. Later, the circulation often 

 becomes feeble. This occurs also in simple MgClj solutions. 



When nine days old the embryos are small and the yolks 

 shrunken. All steps of the fusion of the two eyes into one are 

 shown. This condition makes it certain that the magnesium of 

 the mixture has acted upon the embryos. After fifteen days the 

 eggs are still alive, though small and pale. Thus this double 

 solution is more active than a simple MgClj solution and produces 

 magnesium effects with really less magnesium present than is 

 necessary to give a like result when MgCU acts alone in sea-water. 

 It was stated above that a strength of } m MgClj in sea-water was 

 the weakest solution that caused the one-eyed embryo. The fact 

 that in the mixture aim MgClj sea-water solution gives a like 

 effect may be due to the additional osmotic pressure exerted by the 

 NaCl present as has been suggested by Morgan ('06), to explain 

 similar phenomena in the action of salt solutions on frog eggs. It 

 may also be suggested that the Mg ions act against the Ca ions of 

 the sea-water and thus permit the Na ions to become more active, 

 but this explanation will certainly not apply here, since the embryos 

 show characteristic magnesium effects. 



Eggs were subjected to distilled water solutions of NaCl i m, 

 \ m and | m. During the first day of development many died in 

 most of these solutions. When the eggs were forty-eight hours old 

 the I m solution contained many dead eggs, although the few still 

 ahve were almost normal in appearance. This solution contains 

 only 2.19 per cent NaCl which is less than the amount in normal 

 sea-water yet it is obviously toxic to these eggs. It is evident that 

 other salts present in the sea-water counteract this toxic effect of 

 NaCl. When fourteen days old all of the living embryos appear 

 normal. The f m solution contained one hatched embryo which 

 had a slow pulse and feeble fin movements, it lay at rest on one side 

 but moved if pricked with a needle. In the | m solution of NaCl 



