376 EDMUND B. WILSON 



3. Stage e. The synaptic period. Synizesis 



We now approach a problem that I have thus far found insolu- 

 ble in these animals, and which will therefore be considered very 

 briefly. This involves the changes by which the leptotene-nuclei 

 pass into the pachytene stage, which here begins with the contrac- 

 tion-figure, or synizesis. This stage is initiated by a rapid thick- 

 ening of the threads, accompanied by an increase in staining 

 capacity and a further contraction of the mass which they form. 

 A very good idea of this stage may be obtained from fig. 60, which 

 is carefully studied in every detail. As this figure shows, the 

 synaptic knot distinctly shows two kinds of threads, thick and 

 thin, closely convoluted, but showing no definite polarization or 

 other visible arrangement in loops. The results shows that the 

 process of synapsis must be in progress at this time, but the clos- 

 est study has thus far failed to reveal the true relation of the 

 thick threads to the thin, and I doubt the practicability of deter- 

 mining precisely what is taking place. In these Hemiptera, 

 as Digby has recently remarked of Galtonia, ''synapsis faces one 

 as an unpenetrable wall" ('10, p. 739). A little later thesynaptic 

 knot undergoes still futrher contraction (fig. 61) and is till more 

 difficult to analyze; but in favorable cases it may be seen to con- 

 sist of thick threads, closely convoluted, and still showing no 

 trace of polarization. This stage evidently corresponds to the 

 early pachytene of other forms; but the 'bouquet' figure, so char- 

 acteristic of many animals, seems to be entirely wanting here, 

 and I have found no indication of it in any of the Hemiptera. 



Of one hundred nuclei of this stage in Oncopeltus, taken at 

 random, seventy-five showed X and Y entirely separate, some- 

 times on opposite sides of the synaptic knot, while in twenty-five 

 cases they lay side by side, just in contact. Not one of these 

 nuclei has been found after a search of many hundreds, in which 

 these chromosomes were fused, or even flattened together. In 

 Lygaeus, on the other hand, there is a stronger tendency for these 

 chromosomes to come together at this time, one hundred nuclei 

 showing them separate in forty-five cases and in contact in fifty- 

 five. In the latter case they are often pressed together to form 



