180 WM. REES B. ROBERTSON 



Discussion 219 



1 . V-shaped chromosomes 219 



1. General 219 



2a. V-shaped chromosomes in plant-cell mitoses, not including pro- 

 phase and metaphase of the first maturation division 223 



2b. V-shaped chromosomes in somatic, spermatogonia! and second 



spermatocyte divisions and in anaphases of first spermatocytes 224 



3. V-chromosomes in synapsis and redaction 230 



2. Is there pre-reduction or post-reduction in autosome tetrads? 242 



3. The question of synapsis 246 



1 . Is synapsis a fact? 246 



2. Are the conjugating elements the chromosomes of the last pre- 



meiotic division 248 



3. Is there parasynapsis or telosynapsis or both? 250 



4. Does synapsis lead to fusion of the conjugating elements, or are 



they subsequently disjoined by a reduction division? 251 



4. On the chiasmatype of Janssens 254 



5. Linkage as shown in V-chromosomes — a basis for coupling and repulsion 258 



6. The chromosomes : a mechanism furnishing a basis for variation, heredity 



and evolution? 260 



Bibliography 274 



Explanation of plates 279 



INTRODUCTION 



In a study of the germ cells of the Tettigidae, concerned chiefly 

 with the problem of synapsis, I have found such a surprising 

 uniformity of numbers and size relations among the chromo- 

 somes throughout the eight species of the three different genera 

 examined, that it seems advisable to present the evidence I 

 have on the taxonomic value of the chromosomes and to make 

 my observations on synapsis a second paper, Chromosome 

 Studies. II. 



For purpose of comparison with the Tettigidae, and also to 

 emphasize the constancy of numbers and general size relations 

 in three of the subfamilies of the Acrididae, I have worked 

 out the complexes of Syrbula acuticornis Bruner, and of Chor- 

 thippus (Stenobothrus) curtipennis Harr., two species of the 

 Truxalinae. Stenobothrus has been described by Davis ('08), 

 Gerard ('09), and Meek ('10, '12) as having seventeen chromo- 

 somes. I believe, however, this genus in reality has twenty- 

 three chromosomes, like other genera of the subfamily. 



