Sex Ratio of an Aranead 



447 



Argiopids, Theridiids and Lycosids. In genera like Filistata, 

 where the males are rare and where normal parthenogenesis 

 seems to occur, it may be that the male ratio is smaller than i. 



For Theridium tepidariorum C. Koch I found^ a size differ- 

 ence or dimegaly of the eggs, and concluded it was probable that 

 females emerge from the larger eggs and males from the smaller 

 ones; I showed also that some cocoons contained only large eggs 

 and others only small ones, that therefore some may furnish only 

 females and others only males, and that usually, one kind of egg 

 greatly predominates in number. Unfortunately this species is 

 not found at Austin so that I could not keep females to test this 

 point, and in my collection I have only a few bottles of newly 

 hatched young. These specimens exhibit, however, two kinds of 

 individuals that do not intergrade; ones with larger and more 

 arched abdomina, others with smaller and flatter abdomina; 

 since these correspond respectively with the differences of the 

 adult females and males, I take them to be females and males, 

 respectively. Using this criterion I found the proportion of the 

 sexes of the young from four cocoons to be as follows : 



TABLE III 



These examples are too few to allow any conclusions beyond 

 the one that in a particular cocoon one sex greatly predominates. 

 These relations are quite similar to those found by Doumerc for 

 T. triangulifer, a particular cocoon having a predominance of a 

 particular sex, but quite different from the relations in Latrodectus. 



Therefore there is probably not a common male ratio for all 

 species of spiders. 



' Probable dimorphism of the eggs of an Aranead. Biol. Bull, xii, 1907. 



