78 EDMUND B. WILSON 
relation to the spindle-axis, often lying at right angles to the 
latter. Apparently therefore its duality’ arises quite independ- 
ently of the spindle or astral rays, and its constant position in 
the fully formed spindle is the result of a later adjustment. In 
this species, as in many others, each chromosome is connected with 
the pole by a bundle of delicate fibers. In case of the d-chromo- 
some this bundle is very broad, but I cannot be sure that it is 
double. 
At first sight any observer would, I think, take the d-chromo- 
some to be merely a result of the accidental superposition or close 
adhesion of two separate dyads of unequal size; but such an inter- 
pretation is inadmissible. When all the chromosomes can be 
unmistakably seen, the d-chromosome is found to constitute one 
of the seven separate elements invariably present in this division; 
and since the diploid number is 14 in both sexes this chromosome 
must represent one chromosome, not two, of the original sperma- 
togonial groups. It is certain, therefore, that the double appear- 
ance does not result from close apposition of two separate chromo- 
somes; it is therefore not a ‘‘tetrad” in the ordinary sense of the 
word—+.e., not one that results from the synapsis of two chromo- 
somes that are originally separate in the diploid groups. 
2. The first spermatocyte-division 
This division requires only brief mention. As stated, it shows 
eight separate chromosomes, of which the only one that can be 
positively identified is the Y-chromosome of N. viridula. This 
chromosome, always immediately recognizable in this species 
by its small size (8 c, d, f, g, 2), figs. 12, 18), is usually central in 
position, like the m-chromosome of the Coreidae, but this is not 
invariable. Since it divides equally, and without association with 
any other chromosome (3 g) it is evident that the two idiochro- 
mosomes must be separate and univalent in this division. In N. 
hilaris (8 a, 6, figs. 10, 11) the eight chromosomes usually form an 
irregular ring, there is no central chromosome, and neither idio- 
chromosome can be certainly recognized. It nevertheless seems 
a safe inference from what is seen in N. viridula that the two 
idiochromosomes are here also separate and univalent. 
