HYBRIDS BETWEEN FUNDULUS AND MACKEREL 407 



did there occur isolated eyes and in no other one was there an 

 isolated heart. In none of the other experiments were there 

 quite as numerous green chromatophores, but in two experiments 

 the green pigment approached that described for frequency and 

 brilliance. In three experiments there was a total lack of types 

 in which the head is well developed and the trunk a mere stump, 

 but in four other experiments one or more typical individuals 

 of this sort occurred. In two experiments there was a lack of 

 cyclopeans, but there were numerous individuals with all of the 

 other types of ophthalmic defects. I have no explanation to 

 offer for these minor differences in experimental results. They 

 may have been due to differences in relative vigor of the parent 

 individuals used in the various cross fertilizations. 



DISCUSSION 

 Chromatophore characters as criteria of heredity in Teleost hybrids 



The value of chromatophore characters in the study of hybrid 

 heredity in Teleosts has been abundantly demonstrated in pre- 

 vious papers (Newman, '08, '14, '15; Bancroft, '12). Especially 

 well known are the modes of inheritance of the chromatophores 

 of Fundulus heteroclitus, the square black type and the red type. 

 The branching black chromatophores and the green chromato- 

 phores of the mackerel are not so well known, but are equally 

 characteristic. 



The inheritance of these four different types of chromatophores 

 deserves detailed attention. It seems evident that the black 

 chromatophores in the two species are homologous structures. 

 The differences between the two types is largely a matter of 

 branching habit and size of cell. In Fundulus heteroclitus the 

 cells in their definitive condition are polygonal, almost without 

 branches and frequently fused into syncytia; in the mackerel 

 the body of the cell is insignificant in comparison with the 

 branches, which form an elaborate reticulum, each cell distinct 

 from its neighbors. In hybrids every admixture of the opposed 

 characters may be found sometimes in a single cell, or adjacent 

 cells may show complete segregation of maternal and paternal 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 26, NO. 3 



