NEW TYPES OF CHROMOSOME DISTRIBUTION. 13! 



they appear as separate and distinct individuals in the contraction 

 phase (Fig. 4, K'). A little later (Fig. 4, L) when the chromatin 

 is scattered about through the nucleus, two dark bodies, nearly 

 equal in size, are present. It is very probable that they are both 

 plasmosomes. In one of them, three denser bodies can be 

 faintly, yet unmistakably seen. These are no doubt the three 

 differential chromosomes. The two plasmosomes seem to fuse 

 into one body as in Fig. 4, M, and later condense into a somewhat 

 spherical mass (Fig. 4, N), which persists throughout the greater 

 part of the growth period. The plasmosome goes to pieces in 

 the prophase of the first division and the differential chromo- 

 somes appear at the same time. While in Fig. 4, .17 and N, the 

 differential chromosomes cannot be seen, there is little doubt 

 but that they are present in the plasmosome. From these figures 

 alone, it would be impossible to make the above statement, but 

 in view of the condition in Prionidus, which is described later, 

 I believe the correct interpretation has been given. 



Prionidus cristatus Linn. 



In his suggestive papers of '01 and '06, Montgomery described 

 in Prionidus, the rest stage of the spermatogonia, the spermato- 

 gonial divisions and the rest stage of the primary spermatocytes. 

 For the main part, my observations support his, but as we shall 

 see, he was led to some erroneous conclusions because he did 

 not follow the chromosomes through the first and second 

 divisions. He figures 26 chromosomes in the spermatogonial 

 divisions, and in describing these ('06) he says, "Of the 26 

 chromosomes two are much larger and two much smaller than 

 the others. All these are found on careful inspection to be 

 arrangeable into a series of pairs, in which the two components 



somes ; L, a stage after synapsis, showing two plasmosomes, in one of which 

 the three differential chromosomes can be faintly seen ; M, a stage a little 

 later than L, showing fusion of the two plasmosomes ; N shows the complete 

 fusion of the plasmosomes and the typical appearance of the nucleus through- 

 out the growth period ; O, prophase of the first division the plasmosome has 

 disappeared the three densely staining bodies are the differential chromo- 

 somes ; P, a later prophase, just before the chromosomes arrange themselves 

 in the equatorial plate. K, L, M, N and O are magnified 2,411 diameters; 

 the remainder 3,726 diameters. 



