66 
Psyche 
[March-June 
similar to those found by Beatty (1967) for Adriana : the spine 
count is quite constant within each species, though few specimens 
are actually identical. Furthermore, in the two species of Araneus j 
as in Ariadna , almost no individuals are completely symmetrical in 
pattern, and most are asymmetric in actual spine counts. Beatty 
attributed such differences within and between individuals to develop- 
mental “accidents”; it is clear, however, that in the case of Araneus 
some of the variation between individuals is specifically related to 
difference in size. But for any single specimen the difference in 
spine count (between left and right legs) seems not to be correlated 
with the difference in segment length. (This correlation is cal- 
culated as r 2 in Table in II; the values, though positive, are not sig- 
nificant at the 5% level.) Thus Beatty’s assertion is correct for 
individual spiders; differences between left and right legs do seem 
to be due to developmental accidents, and quite independent of each 
other. This point will be important in the following discussion. 
Discussion 
It is important first to note that the above correlation does not in 
itself imply cause and effect; this is clear from the fact that for any 
individual, segment length and spine count are not correlated. It is 
likely that both the length of the segment and the number of spines 
are dependent on some other factor, such as general body size, etc. 
One obvious possibility is that both measurements are related to 
the degree of development, that is, to the number of molts the spider 
has undergone. In most spiders raised there is some variation in the 
number of preadult instars within a species. Furthermore, it is not 
known with certainty at what stage these spiders mature or how 
many molts occur after maturation, so this possibility cannot be ex- 
amined with the data available. All the calculations here are based 
on sexually mature specimens, but their ages cannot be determined 
more precisely. Consequently, part of the spine count variation may 
be dependent on this unmeasured variable; of course, size is some- 
what dependent on this variable too. 
On the basis of the data presented here, the best statement is 
simply that spine count is very significantly correlated with segment 
length, in these two species of Araneus. 
Then there is the question of geographic variation. The samples 
studied represent a pool of many local populations in North America, 
and it is possible that the relationship between segment length and 
spine count is different in different regions. (Preliminary examina- 
tion of the data with regard to this question indicate that this is in 
