THE GERM-CELLS OF CICADA (TIBICEN) SEPTEMDECIM. 42! 



studied and applies the name "macro-chromosome" to them. 

 Besides the macrochromosome pair, there are usually present one 

 or two chromosome pairs (the BB and CC pairs of Cicada) which 

 are somewhat smaller than the macrochromosome pair, but which 

 can easily be distinguished by their size from the other chromo- 

 somes. The presence of a pair of macrochromosomes and one 

 or two pairs of somewhat smaller chromosomes therefore seems 

 to be characteristic of the diploid chromosome groups of the 

 Homoptera. 



(b] Ring Tetrads. McClung ('14) has described two types of 

 ring tetrads in the Orthoptera which he terms (i) the Hippiscus 

 type, and (2) the Stenobothrus type. Both types of ring tetrads 

 are essentially the same as far as the formation and relation of 

 their elements (chromatids) are concerned. Half of each ring 

 represents a whole chromosome and each univalent chromosome 

 is secondarily split, so that each ring tetrad really consists of two 

 rings superimposed one upon the other. The difference between 

 the two types lies in their relation to the spindle-fiber attach- 

 ments and their position in the metaphase plate. In the Hip- 

 piscus ring type, the spindle-fiber attachments are at the synaptic 

 ends (terminal) and the rings lie flat in the metaphase plate. 

 Consequently polar views of the metaphase plate show the entire 

 ring, while side views show only half of the ring. In the anaphase 

 the two superimposed rings separate and consequently the divi- 

 sion is post-reductional. On the other hand, the rings of the 

 Stenobothrus type usually have median spindle-fiber attachments 

 and the ring lies in the metaphase in the direction of the spindle 

 axis. Only lateral views of the spindle would therefore show the 

 complete ring, while polar views show only half of the ring. In 

 the anaphase the two halves of the ring (which are univalent 

 chromosomes) separate as simple V's and the first maturation 

 division is pre-reductional. 



In Cicada, the large ring of the early prophases is derived from 

 the macrochromosome pair, AA, of the spermatogonia. In the 

 spermatogonial divisions this pair has median spindle-fibre at- 

 tachments and the spindle-fiber attachments of the ring tetrad 

 derived from this pair are also median (Fig. 18). In the meta- 

 phase the ring is arranged on the spindle in the direction of the 



