CHROMOSOME STUDIES 191 



Lires 46 and 49 are of cells from the fat body; 49 of a normal 

 cell, but 46 of a giant cell, in which were found not thirteen but 

 twenty-six chromosomes. The fact that there were twenty- 

 six chromosomes and that among these there were four of each 

 of the six sizes indicates that this is probably a double cell with 

 a double set of cell organs. It may have arisen by fusion of 

 two cells, or by failure of the cell to divide after the nucleus had 

 divided. Cells with multiple numbers of chromosomes occur 

 frequently in this tissue, 



c. Chromosomes in the female. Oogonial or oocyte divisions 

 were not obtained, owing to incompleteness of material, but 

 abundant mitoses were found in the walls of ovarioles. In every 

 case they showed fourteen chromosomes. The x chromosome 

 was distinguishable in over-decolorized cells by its 'woolly' ap- 

 pearance (figs. 51, 53, 55, 58), as was true in spermatogonia. 



At this point it will be well to explain the Tables (I-XX) 

 of chromosome lengths (pp. 193-196), prepared for comparison 

 of the several chromosomes in the following genera and species. 

 These show the relative lengths of the six autochromosomes and 

 the relation that the length of the sex chromosome bears to their 

 combined length. In preparing the tables the length of the 

 image of each chromosome, as drawn at 3900 diameters magnifica- 

 tion, was measured in millimeters. The measurement from the 

 longer member of each pair was used in most cases, since it was 

 evident, by focusing carefully, that apparent difference in length 

 of the members of a pair was due to a fore-shortening of one 

 of the members. When a chromosome appeared in end view, 

 of course its length could not be obtained, and either the chromo- 

 some or the whole cell had to be discarded. 



The chromosomes of somatic cells, spermatogonia, oogonia, 

 and second spermatocytes are rod-shaped and may be measured 

 with little difficulty. Those of first spermatocytes are either 

 cross-shaped or rod-shaped. Here the members of pairs are 

 joined at their distal ends and pulled out in opposite directions 

 at their proximal ends, giving a cross or rod; in the latter the 

 chromosome has double the length of a'spermatogonial chromo- 

 some. To allow a comparison of spermatogonial and somatic 



