AN EXTRA DYAD AND EXTRA TETRAD IN CAMNULA 421 
small per cent of non-disjunctions of its homologous strands. But 
this supernumerary has in all probability been inherited with the 
other members of the complex in one race of Camnula from 1909 
to 1915. It must duplicate a whole or a part of one of the ele- 
ments of the normal complex. Hence its influence on Mendelian 
ratios in any system of allelomorphs, which may be carried by 
it, is obvious, since certain loci may exist in a double, treble, 
quadruple, or quintuple condition. These various valencies of 
the loci in question may all occur, too, in different germ cells of 
the same individual. And if aberrant divisions of the extra ele- 
ment sometimes occur in early somatic mitoses, we have a 
mechanism for the production of mosaics. 
SUMMARY AND CONCLUSION 
In each of five individuals of the genus Camnula from islands 
in Puget Sound numerical variations occur in the chromosome 
group within the gonad. The normal or typical constituents of 
the complex are as constant in number in these animals as in some 
thirty others examined. The inconstant counts are due to 
the varying number of supernumeraries present in different cells 
within an individual. These extra elements are all homologous 
in size, form, and behavior, and are apparently genetically re- 
lated. Within one individual the supernumerary may be absent 
in some complexes, unpaired in some, paired in others, and pres- 
ent in triplicate in still others. If unpaired, the extra element 
usually passes undivided into one of the daughter cells at the first 
maturation mitosis, segregating freely with respect to the acces- 
sory, and dividing like the accessory in the second mitosis. 
Exceptionally the extra dyad may divide in the first mitosis; 
in this case the extra monads pass undivided into one or the 
other spermatid at the second spermatocyte mitosis. If the two 
members of the supernumerary pair are present, they synapse 
like any euchromosome pair in the first spermatocyte generation 
to form a typical tetrad, which behaves in all respects like any 
of the other tetrads. This is in contrast to. the same element 
when unpaired, which then is precocious, like the accessory, in 
