CHROMOSOMES OF MOSQUITO 545 



at the corners so that three masses are formed, each connected 

 to each of the others by. two strands, corresponding apparently 

 to the middles of the original chromosomes. These strands 

 appear at times to have been broken and the three masses to 

 have rounded off into three smooth round 'chromosomes.' All 

 sorts of irregularities of the process, as would be expected, 

 occur. The prophase chromosomes assume all sorts of irregular 

 shapes and the entire contents of the nucleus may be shrunken 

 into a 'synizetic' mass. 



In gonads dissected out and fixed in Flemming the fixation is 

 not by any means at all times perfect. This may be judged 

 in general by the appearance of the tissue as a whole, whether 

 shrunken or not. In some cases, however, the chromosomes 

 appear well fixed, while the tissue may exhibit some degree of 

 shrinkage. Figures 17, 18, and 19 are from one slide in wllich 

 the general fixation was not good. The.homologues are more 

 or less shrunken and appear to touch each other. Figures 16, 

 20, and 21 exhibit the same stage with good fixation. The 

 chromosomes are well separated. 



Under normal conditions it is questionable whether the chromo- 

 somes ever touch each other during mitosis. The parallel union 

 of the members of pairs in first spermatocyte telophase may be 

 an artifact (figs. 68 and 69). In the early telophase of the 

 spermatogonia (fig. 28), the homologues remain distinct. 



The chromatin of the mosquito seems at times to have a tend- 

 ency to flow together. In the cross-shaped tetrads the strands 

 connecting the arms about the opening at the centre would be 

 expected to be of approximately equal thickness — the width of 

 a chromatid. Occasionally one or more of these strands may 

 be reduced to a mere shred, even in prophase, before we would 

 expect any tension upon it. Such a condition is shown by 

 tetrad b of figure 54. 



The contrast between the sharp outlines of the Flemming 

 material (fig. 82) and the picro-formol-acetic fixation of the 

 same stage (figs. 83, 84, and 85) is obvious. In this case the 

 gonads fixed in the latter were dissected out before fixation. 

 The conditions are therefore much better than in those not dis- 



