358 



EDMUND B. WILSON 



F-chromosomes as to apparent size was made in one hundred 

 nuclei, taken at random, from each of the following five stages of 

 the spermatogenesis: (1) the pre-synaptic leptotene, (2) the synap- 

 tic period (synizesis), (3) the post-synaptic spireme, (4) the first 

 spermatocyte-metaphase, (5) the second spermatocyte-metaphase. 

 The best of these stages for the purpose are the maturation-divi- 

 sions as seen in side-view (because of the elimination of foreshort- 

 ening) and the pre-synaptic leptotene (because of the clearness 

 with which both sex-chromosomes may be seen at this time), but 

 in neither individual was the requisite number of side-views of the 

 first division available. In the latter case, therefore, both side- 

 views and polar views have been included. The cases are classed 

 as equal (eq.), unequal (uneq.) and doubtful (dbf.), the latter 

 including those in which there was reason to suspect error due to 

 foreshortening or the like. 



There is no doubt a considerable error in these figures due to 

 foreshortening, since these chromosomes, though often spheroidal, 

 are often slightly elongated (elhpsoidal), and are of course seen 

 in all positions. But after making a large allowance for this, the 

 contrast between the two individuals is manifest at every stage 

 of the spermatogenesis, and nowhere more so than in side-views 

 of the second division. I have made tabulations of several other 

 individuals which give percentages of equality ranging from ninety 

 down to ten; but in most cases the data from intermediate types 

 are less consistent and the probable error is much larger, for 

 obvious reasons.^ 



From these observations I draw the conclusion that in Onco- 

 peltus the X- and F-chromosomes show a certain tendency 



'" Compare figs. 9, 10, 14, 15, 24, 25 (equal type, no. 711), 18, 19,3 6-40 (equal type, 

 no. 712) with 11, 12, 16, 17, 20, 31, 32, 42 to 44 (unequal type, no. 760). See also 

 photos. 7 to 11. 



