398 H. H. NEWMAN 



plasm would not be expected to activate so readily another 

 species of protoplasm. It might conceivably retard develop- 

 ment beyond the normal rate even in a slowly developing egg 

 and still play the typical role of sperm materials in heredity. This 

 is, I believe, exactly what happens in all heterogenic hybrids, 

 for they all exhibit more or less pronounced evidences of early 

 and long-continued retardation. That the sperm actually do 

 cooperate in development even in suborder crosses is shown by the 

 unmistakable cases of paternal heredity. It is inconceivable 

 that a foreign sperm could function in heredity without effective 

 functioning in development, and any hybrid in which paternal 

 heredity is demonstrated is neither a parthenogenetic individual 

 nor pure maternal. 



It is just exactly this point that the present experiments 

 demonstrate, to my mind at least, beyond controversy. I have 

 selected the Fundulus X Mackerel cross out of nearly one hun- 

 dred crosses that I have personally made among the Teleosts 

 because it is especially favorable. In no sense, however, is it 

 exceptional or peculiar in character, merely a little clearer and 

 more diagrammatic than others that might have been chosen. 

 Any one of half a dozen other crosses would have done nearly as 

 well. 



II. EXPERIMENTAL 



Differences between adults of Fundulus heteroclitus and Scomber 



scombrus 



Fundulus and the mackerel are sharply contrasted in all of their 

 adult characters as might be expected in representatives of differ- 

 ent suborders. They differ radically in habitat, ecological 

 relations, breeding habits, eggs, and larvae. Fundulus is a 

 minnow with shore-feeding habits, is found in both salt and brack- 

 ish water, is tolerant of foulness in water and to low oxygen and 

 high CO2 concentration. The large eggs (2| mm. in diameter) 

 are laid during a clasping act on the part of the male which 

 insures fertilization of the eggs with a minimum expenditure of 

 milt. The eggs sink to the bottom and adhere to stones and 

 seaweeds at or near the bottom by means of the sticky egg 



