104 
Psyche 
[March 
Thus it is clear that both female and male behavior patterns in R. 
jnetallica are well adapted to secure outcrossing among colonies as a 
usual condition of the mating flight. Furthermore, multiple insemi- 
nation of one worker, and insemination of more than one worker by a 
single male, can occur. The related question of whether a single 
worker can be inseminated several separate times during its life span 
has not yet been answered, nor has the question of whether new- 
hatched workers, after insemination, may return permanently to the 
parent colony to add to its reproductive potential and prolong its life 
beyond the limit of two generations so usual in Formicid communities. 
It may be suggestive in this connection, however, that not all of the 
worker spermathecae that contained sperm were found by Whelden to 
be filled. Indeed, of 22 individuals of R. violacea found to contain 
sperm, among a sample of 274 examined, in only two were the sperma- 
thecae completely occupied by a dense sperm ball of cells. In three 
individuals the sperm mass was very small and loose, comprising only 
an estimated 50-100 cells. In the remaining cases, the spermathecae 
were partially filled, though fully inflated. 
All the evidence seems very suggestive that a rather high degree of 
heterozygosity must indeed be regularly maintained in colonies of R . 
met allica, involving the germplasm of populations greatly exceeding 
the single colony in numbers. It became of considerable interest, 
therefore, to enquire what might be the limits of viability in a single 
colony where strict inbreeding was enforced over several worker 
generations. 
TOLERANCE OF RHYTIDPONERA METALLICA TO 
EXTENSIVE INBREEDING 
In this context, certain further observations made on the colony of 
R. metallica already cited may be of interest. As already described, 
this colony was maintained throughout the ten years of its existence 
as a set of “closed” populations, from which no individuals could 
escape and which none could enter from the outside. By the time that 
its two longer-lived sections died out, at ages respectively of 9 years 
6 months and 10 years 2 months, many new generations of workers 
had been matured, to be fertilized in turn by successive generations of 
males of the same colony. It is not possible to assess quantitatively the 
degree of homozygosity finally attained in these two populations. It 
must have increased very considerably, however, over the years. It is 
therefore of special interest to note that in the last months of the lives 
of both sections ova, although continuing to be produced in numbers, 
characteristically failed to hatch larvae. A cytological examination of 
these eggs by Whelden (unpublished) showed a high degree of 
