148 T. H. MONTGOMERY, JR. 



spermatogonia, sometimes paired ? When they are unpaired 

 they are larger than the other chromosomes. This might imply 

 that such an unpaired heterochromosome really represents two in 

 close union, /'. c., is already bivalent in the spermatogonium. 

 And this I think is a very probable explanation, in view, first, of 

 the behavior of the unpaired chromosomes during the growth 

 period of the spermatocyte in Protcnor (fully described in my 

 paper, "The Germ Cells of the Metazoa") ; and, second, of the 

 fact that such a chromosome sometimes shows a distinct con- 

 striction at its middle (shown for Haruwstes in my paper, 

 " Further Studies on the Chromosomes," etc.). 



It is hoped that these considerations, in endeavoring to show 

 the likenesses and differences of the two kinds of heterochromo- 

 somes, will bring more uniformity in the interpretation of these 

 modified chromosomes, and that such chromosomes should always 

 be taken into account in any discussion of the idea of the indi- 

 viduality of the chromosomes. 



4. THE CONJUGATION OF THE CHROMOSOMES IN THE SYNAPSIS 

 STAGE, AND ITS RELATION TO THE REDUCTION DIVISION. 



It is now determined for a considerable number of cases that 

 in the early portion of the growth period of both ovocytes and 

 spermatocytes there takes place the process known as the " re- 

 duction in number" of the chromosomes. Thus if there are 

 twenty-four chromosomes in the spermatogonium, twelve are 

 found in the maturation period before the first mitosis. This 

 fact was first established by Boveri (" Zellen-Studien," /. c.) and 

 by Brauer. 1 Really the name applied is a misnomer, for there is 

 no loss of chromosomes, no true " reduction " in this number, 

 but it is a conjugation of the chromosomes. Riickert 2 sought to 

 explain it by stating that in the prophase of the first maturation 

 division the chromatin spirem breaks into only half the normal 

 number of segments. This, however, is inadequate as an ex- 

 planation, for I showed in the " Spermatogenesis of Peripatus " 

 that in the prophases of the first maturation mitosis there is a 



1 " Zur Kenntniss der Spermatogenese von Ascaris megalocephala,".4;r/z. J///J-;-. 

 Anat., 42, 1893. 



2 " Zur Eireifung bei Copepoden," Anat. Heftz, 4, 1894. 



