288 Charles R. Stockard 



solutions of the proper strengths and the eggs were either killed or 

 unaffected. After a few experiments, however, a strength of 

 MgClj in sea-water was found that gave a large percentage of 

 cyclopia, in many cases again causing 50 per cent of the eggs to 

 form such individuals. This was a if M solution prepared as 

 follows: 19 cc. of a molecular solution of MgClj in distilled water 

 was added to 41 cc. of sea-water. This is not then an actual 

 if M MgClj solution but it is if parts molecular MgClj. Mak- 

 ing the solution in this way adds to the sea-water, water lacking 

 all of its constituents except the Mg and thus increases in a greater 

 proportion the excess of Mg present. 



Cyclopia occurred in a series of similarly prepared solutions 

 ranging as follows: |f m, if m, if m, ff m, |f m, ff m and || m 

 MgClz- A point of importance is that the proportion of cyclops 

 embryos produced gradually rises in this series up to the ff M 

 solution and then falls off again. To illustrate concretely, in 

 Experiment VII the if M solution caused 12 per cent of the eggs 

 to form Cyclopean embryos, the if M gave 30 per cent, the if M 

 22 per cent, while ff M gave 50 per cent with the cyclopean defect. 

 Continuing the series, the |f M falls off to 30 per cent and the 

 |i M gives 23 per cent, while in the |f M no cyclopia occurred and 

 the eggs were all killed. It must be born in mind that these 

 percentages are for the eggs that formed embryos and not for 

 the total number of eggs first put into the solution. The peculiar 

 fact is, that in a series of MgClj solutions we reach a place where 

 a maximum number of cyclopean embryos occur and in strengths 

 both weaker and stronger than this the number of cyclopean 

 individuals is less. If the defect is due to osmotic pressure, we 

 should not expect a greater pressure to bring about a more normal 

 development. If the action is chemical, we do not usually reach 

 a chemically effective dose and find that a greater dose is less 

 effective. It might be argued that below the point of maximum 

 occurrence of the cyclopean defect, the solutions are insufficient 

 to effect any but the weaker embryos, so that a small number of 

 cyclops appear; above this point the solutions are so strong that 

 all except the hardiest embryos die in early stages and those sur- 

 viving are so resistant that only a few give the cyclopean defect. 



