THE CELL AND CELL DIVISION 75 



chromosome groups derived from the egg and sperm nuclei, each of S 



st 



chromosomes, remain distinguishable through a considerable series of 

 the early divisions of the zygote; two separate spiremes, each forming 



s chromosomes, may even be distinguished sometimes (Ruckert). 

 And in some hybrids where the chromosomes are unlike in number, or 



ill 



.it'-'V.^'v^'; 



Hi ?: .<* 



^ ../.\> 

 ^T. 



.; 



H 



FIG. 39. The chromosome group in the hybrids of the Teleosts, Fundulus and 

 Menidia, showing the distinctness of the paternal and maternal elements. From 

 Moenkhaus. A. Late anaphase of first cleavage of normally fertilized Fundulus. 

 All chromosomes of the long type. B. Anaphase of first cleavage of normally 

 fertilized egg of Menidia. All chromosomes of the short type. C. Anaphase of 

 first cleavage of Fundulus egg fertilized with Menidia sperm. To the left long 

 (Fundulus) chromosomes only, to the right short (Menidia) chromosomes only. 



D. Anaphase of first cleavage of Menidia egg fertilized with Fundulus sperm. 



E. Metaphase of first cleavage of Fundulus egg fertilized with Menidia sperm. 

 d\ chromosomes of paternal origin. 9 , chromosomes of maternal origin. 



form, or size, the two groups derived from the male and female parents 

 remain distinct (Fig. 39), often for a very long time, perhaps even 

 throughout life (Moenkhaus, Herbst, Baltzer). 



While evidence of the kind suggested above does not constitute 

 definite proof of the genetic continuity of the chromosomes, it is very 

 difficult to explain the facts upon any other basis. In the absence of any 

 other satisfactory hypothesis in this field it seems wise to accept a 

 certain modification of the essential idea, as a working basis, while 

 admitting the difficulties of demonstration and the existence of some 

 apparent contradictions. We may recognize in this difference of opinion 



