I5O T. H. MONTGOMERY, JR. 



Now I reached the conclusion ("A Study of the Chromo- 

 somes," etc.) that in the synapsis stage there is effected a 

 conjugation of paternal with maternal chromosomes ; under 

 "paternal " understanding those derived from the spermatozoon, 

 and under "maternal," those from the ovotid. The arguments 

 for this were stated as follows : 



1. In Ascaris megaloccpliala itnivalcns there is the normal num- 

 ber of two chromosomes. The ovotid and spermatid have each 

 only one. In the fertilized egg there is one derived from the sper- 

 matid, one from the ovotid ; therefore the bivalent chomosome 

 found in the maturation period of the spermatocyte or ovocyte 

 must have been formed by the conjugation of a paternal with a 

 maternal chromosome. 



2. In the spermatogenesis of the Hemiptera there are usually 

 two small heterochromosomes in the spermatogonia. These unite 

 to form a bivalent one in the spermatocyte. They become 

 separated from each other in the first maturation mitosis so that 

 no spermatid receives more than one. Evidently then in the 

 fertilized ovum since only one comes from the spermatid, the 

 other must come from the ovitid. Therefore in the conjugation 

 of the two in the synapsis, it is a conjugation of a paternal one 

 with a maternal one. That was reasoned out without any 

 knowledge of such chromosomes of the ovogenesis. Now I 

 add Fig. 15, showing among the chromosomes of an.ovogenic 

 monaster stage the two small elements N and ;/, which are 

 heterochromosomes of the same number and size as those found 

 in the spermatogonium (Fig. 16, N, ;/). Therefore, there must 

 be a conjugation in the ovogenetic synapsis stage, as well as 

 in the spermatogenetic, of a paternal heterochromosome with a 

 maternal one. 



3. That besides the heterochromosomes, whenever there is 

 recognizable in the spermatogonic chromosomal plate a pair of 

 chromosomes notably different from the others in volume, there 

 is always found in the first maturation mitosis a particular bivalent 

 chromosome notably different in volume from the other ones, 

 and so evidently formed in the synapsis by the conjugation of 

 the two peculiar univalent ones of the spermatogonium. This 

 bivalent chromosome is so placed in the first maturation spindle 



