normalities were produced. This difference is 

 perplexing, and is probably due to genetic dif- 

 ferences among individuals of this species in 

 susceptibility to the chemicals. This is more 

 understandable when it is realized that rela- 

 tively few females can supply all the eggs needed 

 for an entire experiment. Such variability in 

 response makes this species a poor one to use in 

 teratological studies. 



Effects were seen at dosages as low as 10 ppb. 

 These are levels far lower than those which pro- 

 duced noticeable effects in Fundulus heteroclitus 

 embryos (Weis and Weis 1974) in which it was 

 necessary to increase the dosage to parts per mil- 

 lion. This may be due to differential permeability 

 of the chorions of the two species and/or to a 

 higher general resistance of Fundulus which is 

 generally considered a hardier fish than Menidia. 

 The dose levels which affected Menidia are levels 

 near those which have been found temporarily, in 

 solution or suspension, in natural areas (Finley et 

 al. 1970; Kennedy and Walsh 1970). Therefore 

 these adverse effects could occur during the de- 

 velopment of fish embryos in nature. 



Acknowledgments 



We thank John C. Baiardi, Director of the New 

 York Ocean Science Laboratory for making 

 facilities available to us. We are especially grate- 

 ful to Eugene Premuzic and John P. Wourms for 

 sharing their laboratory and advice. Thanks are 

 also extended to S. H. Gilani for reviewing our 

 manuscript. 



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JUDITH S. WEIS 



Department of Zoology and Physiology 

 Rutgers University 

 Newark, NJ 07102 



peddrick Weis 



Department of Anatomy 



College of Medicine and Dentistry of New Jersey 



Newark, NJ 07103 



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