PRODUCTION OF MONSTERS BY HYBRIDIZATION. 309 



fact that the same series of subnormal types (monsters) are found 

 in a great variety of different crosses, and also by the fact that 

 these same abnormal types may be produced by purely physical 

 or by chemical agents. 



OTHER METHODS OF PRODUCING MONSTERS. 



As long ago as 1907, Stockard, by the use of solutions of 

 magnesium chlorid, was able to produce, among other abnormal 

 conditions, a considerable percentage of cyclopic and allied 

 ophthalmic terata. Although little was said about abnormal 

 conditions other than those associated with the particular terata 

 mentioned, enough data was given to show that many if not 

 all of the other well-known conditions occurred. 



In 1909 and 1910 Stockard contributed further papers con- 

 cerning the development of teratomata, showing that the same 

 results could be obtained with alcohol and other anaesthetics. 

 He called particular attention to ophthalmic terata, making it 

 clear that the eye anlages appear to be especially susceptible to 

 anaesthetics, and explained cyclopia and similar conditions as 

 "the result of an anaesthetic action during the early develop- 

 mental stages." Later, when McClendon ('12) obtained a 

 similar series of eye defects by the use of substances that are 

 non-anaesthetic in action, Stockard took the more general view 

 that deleterious chemical substances merely lower the vitality 

 of certain sensitive anlages and cause arrested development of 

 important structures. Stockard implies that the results are 

 primarily due to a lowering of developmental rate. The paired 

 eyes for example are believed to arise from an unpaired median 

 anlage which normally undergoes a sort of twinning process 

 producing two eyes. Under the influence of deleterious chemi- 

 cals "the median anlage does not widen or spread laterally but 

 is arrested in its primary median condition." Hence the un- 

 paired cyclopean eye develops. 



Recently Werber (1915, 1916) in three papers and especially 

 in his latest one (1916) re-attacked the problem from a some- 

 what novel point of view. Starting in with the assumption 

 that the development of monsters in mammals is caused by 

 "pathologic parental metabolism" he decided to test his hypo- 



