354 LOUIS I. DUBLIN. 



generally present in the late cleavage stages of the hybrid teleost 

 embryo, the parental chromosomes are positively not separated 

 into two groups. Thus during and after the third cleavage of 

 the egg, the long and the short chromosomes of the two parents 

 of the hybrid mingle together, the spindles never again showing 

 any division into right and left sides with the corresponding sep- 

 aration of the chromosomes, according to the work of Hacker, 

 so marked in the early divisions of the copepod egg. The 

 double nucleolate condition, cannot, therefore, be taken as an 

 indication of the autonomy of the paternal and maternal con- 

 tributions. 



In Pcdiccllina, moreover, the fertilization and early cleavage 

 stages, where the autonomy of the parental chromatins would be 

 most marked if at all present, is not at all in evidence. In spite 

 of the bi-nucleolate condition of the later life history, it is clear 

 from the early stages that the chromosomes of the egg and the 

 sperm have, as in the Fundulus-Menidia hybrid of Moenkhaus, 

 entirely mingled, perhaps in the first cleavage spindle. Thus, 

 also in Ascaris, according to Zoja, '95, where the chromosomes 

 of the egg and sperm have mingled as early as the I 2-cell stage. 

 In the Copepods themselves, it is not clear that the physiological 

 distinction in the parental sides of the spindles persists after the 

 early cleavages, and thus, the only important evidence for per- 

 sistent gonomery is, in these types, the constant appearance of 

 the two nucleoli, and this, it is clear, involves an assumption 

 which, in view of the latest work, is full of difficulties. Of still 

 less weight is the occurrence of bilobed nuclei in the late stages, 

 these probably representing little more than an intermediate stage 

 in the fusion of the several vesicles into one resting nucleus. 

 The appearance of the double spirem in the early germ-cells 

 while of greater value is, from the rarity of its occurrence and 

 from the want of proof that the halves are parentally different, 

 also indecisive. 



It is therefore much more probable that the parental chromo- 

 somes actually mingle among themselves at an early period of 

 development, and that these so-called outward expressions of 

 internal independence are either accidental and unconnected with 

 the chromatin phenomena or are expressive of other conditions 



