THE PROCESS OF HEREDITY AS EXHIBITED BY THE 

 DEVELOPMENT OF FUNDULUS HYBRIDS^ 



BY 



H. H. NEWMAN 



With Five Plates and Sixteen Figures in the Text 



I Introduction 504 



II Material and methods jo6 



A Materials — A description of the species used 506 



1 Morphological differences between the adults 506 



2 Physiological differences between the adults 507 



3 Morphological differences between the eggs and embryos 507 



4 Physiological differences between the eggs and embryos 508 



B Methods 509 



1 Spawning behavior and sexual dimorphism 509 



2 The importanceof equalizing the physiological condition of the parents 510 



3 The importanceof equalizing the external conditions of the developing embryros .. 512 



4 The attitude that must be taken toward variability 512 



5 Methods proper 514 



III Description of Experiments and Presentation of Data 517 



A Data derived from the study of living material 517 



1 Type series (Series I) 517 



2 Other series (Series 2 to 6) 531 



3 Fragmentary data (Series A to H) .• 537 



B Data derived from the examination of preser\-ed material 539 



1 Rates of cleavage 539 



2 Later stages 540 



C Experimental data 542 



1 Resistance to lack of oxygen 542 



2 Experiments with KCN 545 



IV Summary of data 547 



V Discussion 550 



A The relative influence of maternal and paternal elements in determining the characters 



seen in early development 550 



B Exclusive versus blended inheritance 552 



C Dominance and sur\'ival 556 



D High degree of variability in hybrid strains the result of varying degrees of compatibility 



between the germ cells of the two species 557 



E The rhythmic flux of characters 558 



F The importance of external factors in heredity 559 



1 Contributions from the Zoological Laboratory, University of Michigan (No. 116), and from the 



V oods Hole Marine Biological Laboratory. 



The Journal of Experimental Zoology, vol. v. no. 4 



