PLATE 18 



EXPLANATION OF FIGURES 



148 to 160 Syrbula acuticornis Bruner. 



148 Metaphase of spermatogonium. Autosomes paired from 1 to 11 accord- 

 ing to size. Sex chromosome (lOx) numbered 10 to show that it ranks tenth in 

 size, being between the ninth and tenth autosomes; marked x to indicate its 

 sex determining nature. 



149 to 158 First spermatocyte stages. 



149a Early prophase of first spermatocyte stage h . Four of the paired chro- 

 mosomes coming out of parasynapsis. x, x, indicate the points from which the 

 attraction fibers will spring in the succeeding reduction division. 



149b Remainder of the nucleus of the spermatocyte shown in figure 149a 

 (the following section). In the cell shown in figures 149a and 149b the eleven 

 paired autosomes and the sex chromosomes are all accounted for. 



150a and 150b Two successive sections of a spermatocyte at a stage (z), 

 later than that shown in figure 149. The four parts of the paired chromosomes 

 are evident. Chromosomes are condensing to enter the metaphase. 



151 Portion of a nucleus showing the four parts of paired chromosomes 1, 2, 

 5, 11, and the continuation of the separation process following parasynapsis. 

 Stage h. 



152a to 152d Stage i. Individual chromosomes from different cells show- 

 ing further continuation of the process of separation and the structure of the 

 various paired autosomes about ready to enter the condensed metaphase stage. 

 The attraction fiber knobs, i.e., the exconjugating knobs of the tetrad, are in- 

 dicated by X, X. 152a would have formed a ring, 152b a cross, 152c a V with two 

 knobs at the apex, and 152d a rod chromosome. 



314 



