210 CHARLES L. PARMENTER 



spermatogenesis from the early spermatogonia to the spermatids. 

 He thus demonstrates that the conjugating elements are chro- 

 mosomes and are morphologically identical with the spermat- 

 ogonial chromosomes. That one of the homologues of each 

 conjugated pair is maternal and the other paternal is very 

 probable, as has been shown by the observations of Van Beneden 

 ('83) and numerous later authors, especially Mulsow ('12). 



It remains to be seen whether the pairs of maternal and 

 paternal homologues present in the germ cells during the matura- 

 tion period maintain their identity in the germinal line between 

 the time of fertilization and the first observations upon the sper- 

 matogonia. This has been accomplished in part. AIulsow ('12) 

 has followed the actual chromosomes of the living spermatozoon 

 of a parasitic trematode, Ancyracanthus, into the egg, and has 

 found the expected number of chromosomes in the two pro- 

 nuclei and cleavage stages. He also observes that the chromo- 

 somes of the cleavage nuclei show in many cases a tendency to 

 lie parallel to one another, and suggests that this is an approxi- 

 mation of maternal and paternal chromosomes. Boveri ('87, 

 '92) traced the chromosomes of the primordial germ cell of Ascaris 

 univalens through the cleavages from the two-celled stage, 

 and Moenkhaus ('04), Morris ('14), Richards ('17) have traced 

 the persistence of individual chromosomes through several 

 cleavages of hybrid eggs of Fundulus. If this persistence of the 

 chromosomes is permanently maintained, the observations of the 

 above authors make it probable that the maternal and paternal 

 chromosonies form a duplicate series throughout the germinal 

 line. 



b. Pairs in somatic cells. Since the existence of chromosome 

 pairs can be considered to be all but proved throughout the 

 germinal line, it remains to be seen whether or not the chromo- 

 somes of the somatic cells, which are really descendants of those 

 of the germinal line, still retain this duplicate series and thus give 

 evidence of maintaining their individuality. 



The earliest observations bearing upon this question were 

 made on Salamandra maculosa by Flemming ('82) and Rabl 

 ('85), who observed that the chromosome segments were not of 



