264 V»^M. REES B. ROBERTSON 



predominating tendency for the four-strand tetrads to divide 

 throughout a large part of their length along the plane of the 

 primary split (/), the division beginning at the proximal end, 

 and the halves remaining attached at the distal ends. There 

 results the dumb-bell shaped rods (figs, 29-31, 73-77, etc.) 

 of the late prophase and the metaphase. Frequently in the 

 longer chromosomes of Tettigidea there is a tendency for a tet- 

 rad simultaneously to split also from the distal end along the 

 plane of the second division, so that there is formed a cross with 

 unequal arms (figs. 94-99, 112-114), the transverse arms being 

 short, even mere knobs. For the Tettigidae the characteristic 

 form of prophase tetrads in tetrads formed from shorter chromo- 

 some pairs is the dumb-bell rod, and in tetrads from longer 

 chromosomes it is the cross with very short transverse arms. 

 In the species of the subfamilies having twenty-three chromo- 

 somes, there is a prevailing tendency in the pure straight-rod 

 type for the longer and intermediate chromosome tetrads to 

 split widely along the plane of the secondary division. If this 

 begins at the distal end and extends almost to the proximal 

 end the result is the V-tetrad (fig. 157, no. 10, and Robertson, 

 '08, plate 21, chromosomes 4, 6, 8); if it does not begin at the 

 distal end, but at a point just proximal to it, and extends as be- 

 fore nearly to the proximal end, there results a horizontal ring 

 (11 in fig. 157 and Robertson, '08, plate 21, chromosomes 7, 

 9-12) ; or, .in the case of the intermediate chromosome pairs, 

 if the widening of the primary split, beginning at the proximal 

 end, is equal to that of the secondary beginning at the distal 

 end, a cross tetrad results. The three smallest tetrads usually 

 form dumb-bell shaped tetrads, as in Tettigidae (Robertson, 

 '08, plate 21, chromosomes 1-3). Chromosomes of the ring- 

 V-tetrad-, and cross-type are characteristic for these subfamilies, 

 while those of the dumb-bell-, rod-, and unequal-armed cross- 

 type are characteristic for the Tettigidae. The behavior of 

 tetrads in producing these forms is not such a constant char- 

 acteristic, however, as is number or size. This may be seen in 

 my chromosome table ('08, plate 21). While there is a tendency 

 to produce tetrads of a certain form, rings for instance, in no. 10, 



