10,2 ROBERT H. BOWEN. 



point was studied with special care. Two metaphase plates in 

 polar view were found in which the chromosomes could be readily 

 counted, although both were a trifle irregular in arrangement. 

 One of these plates (Fig. n) seemed to be in the final stage of 

 formation, and some of the chromosomes were still not completely 

 oriented. Fortunately this was particularly true of the Y chromo- 

 comes, whose constitution was thus rigorously demonstrated. In 

 the normal cells the Y chromosome is represented by a dyad which 

 is divided in the first spermatocyte division (see Montgomery, 'n, 

 Fig. 94). In a tetraploid cell we should expect to find two such 

 dyads, and this is actually found to be the case. The Y chromo- 

 somes have not conjugated, but each has behaved exactly as 

 though the other were absent. The parts of the dyad have been 

 in each case precociously separated (Fig. n). Furthermore, two 

 unusually large chromosomes can be readily picked out (A and 

 A'}, and these seem to correspond to the single large chromosome 

 of the normal haploid plate (see Wilson, '050, Fig. 30). A count 

 of all the chromosomes (counting the Y dyads each as a single 

 chromosome) gives a total of 17 one more than the expected 

 number (16, or 8 times 2). It seems likely that the extra chromo- 

 some may be due to the counting of an A" dyad, the parts of 

 which have become separated, as two chromosomes instead of a 

 single one. In Fig. 12 another plate is given which, judging 

 from its neighbors, is probably in a very early anaphase stage. 

 The plate is somewhat more compact, and the Y chromosomes, 

 now presumably being drawn apart, are seen as single chromo- 

 somes. In this plate 16 chromosomes are clearly to be counted, 

 although one of them is irregularly placed. 



Unfortunately no second maturation divisions were found, so 

 that it was impossible to check up the behavior of the X and Y 

 chromosomes in that division. The spermatids seem to be normal 

 in every way, except that they are larger than is usual ; and at 

 least the earlier stages of differentiation are gone through in a 

 normal manner. Subsequently, some of them certainly become 

 abnormal, but so do some of the sperm in an adjacent lobe (No. 

 6) ; and it is, therefore, impossible to tell whether the degenera- 

 tion is connected with the tetraploid condition or not. 



