172 Changing Plant and Animal Nature 



Dr. Stockard modified the chemical composition of sea 

 water in which the eggs of the small minnow Fundulus were 

 hatching by increasing the proportion of magnesium salts. 



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lizu 



Fig. 45. Chemical Modification of Development 



These cyclopean minnows are strikingly different in appearance from the two- 

 eyed individuals with which we are familiar (two-eyed larva at top). The de- 

 velopment of eggs from a given batch into one type or the other can be 

 controlled by regulating the proportion of magnesium in the sea water. After 

 Stockard. 



When the ratio of magnesium to sodium exceeds a certain 

 point, the young fish hatched out with a single eye in the 

 middle of the forehead instead of the usual two eyes on the 

 sides (Fig. 45). 



