PROBABLE DIMORPHISM OF THE EGGS OF AN ARANEAD. I I/ 



almost all the eggs of no. 800 (fixed at the same age) were 

 larger than the eggs of no. 722 (fixed at the age of I ^ hours), 

 but a few eggs of no. 800 were as small as the eggs of no. 722. 

 The same held for the successive cocoons of four other spiders. 

 Then in one cocoon collected in the wild state, not raised in cap- 

 tivity, there were 596 eggs (the largest number I have found in 

 any single cocoon) ; most of these could, with certainty, be 

 ranked as large eggs (about 478) while about 118 of the eggs 

 were clearly small eggs, but a few were intermediate in size be- 

 tween these two groups. The latter case is important in showing 

 that while intermediate sizes may occur between the large and 

 the small eggs, in the same cocoon or in successive cocoons, the 

 intermediates are very few in number compared with the ex- 

 tremes, a condition that would not occur in simple individual 

 variation. 



The conclusions permitted by these observations are as follows : 

 This species of Theridium produces large eggs and small eggs ; 

 in one cocoon all may be large or all may be small, or in any one 

 cocoon both kinds may occur ; intermediates in size are relatively 

 very infrequent. Such a difference of volume might be termed 

 " dimegaly " for convenience, especially when no structural dif- 

 ferences are found or known to accompany this difference in 

 volume. But there is a possibility if not a probability that this 

 dimegaly may be dimorphism, and that females develop from the 

 large eggs and males from the small ones. The adult female 

 spiders are considerably larger than the adult males, notably 

 with regard to the dimensions of the abdomen. The occurrence 

 of occasional intermediates between the two kinds of eggs may be 

 readily explained by the fact that in each kind of eggs there is 

 always some individual variation in volume, in conjunction with 

 the assumption that the smallest extremes of the larger kind 

 may not be larger than the largest extremes of the smaller. In 

 those cases where some cocoons contain only large eggs, others 

 only small ones, there would then be instances where some 

 cocoons produce only females and others only males. Further, 

 if this dimegaly is really dimorphism, a conclusion, that we are 

 tentatively maintaining, then in a succession of cocoons made by 

 the same spider there would be batches of female eggs only 



