AN EXTRA DYAD AND EXTRA TETRAD IN CAMNULA 413 
mosome pair, a member of which it resembled in size and form, 
to form a hexad in metaphase; he therefore identified it as an 
extra m-chromosome. An unpaired supernumerary in Tetti- 
gidea which behaved like the accessory in the growth stages and 
had a tendency to synapse with the latter in these stages, was iden- 
tified by Robertson (’17) as a deficient extra accessory. Stevens 
(08, 712 a, ’12 b) in Ceuthophilus and Diabrotica, and Carothers 
(17) in Trimerotropis and Circotettix, describe unpaired super- 
numeraries which simulate the behavior of the sex chromosomes 
in the growth stages, but show no tendency to couple with the 
latter. Stevens believed the supernumeraries she described were 
derivatives of the sex chromosomes, but Carothers is not in- 
clined to identify the extra elements in Trimerotropis and Circo- 
tettix with the accessory. 
In Camnula neither the unpaired supernumerary nor the extra 
tetrad have as yet been carefully studied in the early growth 
stages. In the later prophases of the first spermatocyte mitosis, 
the extra element, as we have seen, if unpaired, simulates the be- 
havior of the accessory; if paired, it behaves like any euchro- 
mosome tetrad. In this instance precocity in the extra dyad 
seems to be due simply to its unbalanced condition, and does not 
necessarily indicate relationship with the accessory. The close 
resemblance which the extra tetrad sometimes bears to tetrad 
no. 3 has been pointed out. I believe by careful study of the 
earlier growth stages, and by breeding the animals, the derivation 
of the camnulan supernumerary can be demonstrated. Until 
this work has been attempted, it seems better not to speculate 
farther concerning the origin of the element in question. 
Given a particular unpaired supernumerary, present in the 
germ cells of several individuals of a race occupying a limited area, 
it will happen sooner or later that two gametes, each containing 
this element, will conjugate. The resulting zygote will have 
naturally, a homologous pair of extra chromosomes. ‘These 
may synapse in maturation in the typical manner to form tetrads 
as in Camnula, or may unite with the element from which they 
were originally derived to form multiples of a higher valence, as 
in Metapodius (Wilson, ’09 b, 710). 
