Sex Ratio of an Aranead 44.C 



Table II the average number for each series, for the 127 cocoons 

 from which young emerged; 2871 eggs were infertile in the 127 

 cocoons from which hatched 41,749 spiderlings. Were those 

 undeveloped eggs all males, the male ratio would be increased to 

 8.8; were they all females, decreased to 5.1; yet there is no prob- 

 ability of either of these extreme cases. For when the male ratio 

 is unusually high (30 or higher) the number of unhatched eggs 

 to a cocoon is small, and where the male ratio is unusually small, 

 a good case of which is the series 2031 of Table I, the number of 

 unhatched eggs is generally but not always very high. Therefore 

 it is probable that a large proportion of such undeveloped eggs 

 are males, and consequently the error introduced by such eggs is 

 probably a small one. 



Next, as to the cause of lack of development of certain eggs. 

 Mechanical jarring of the freshly laid eggs of spiders has been 

 proved to be fatal to them ever since the observations of Herold, 

 so that the handling of the cocoons in the removal from the cage to 

 the hatching bottle may have prevented the development of some 

 eggs. Yet I believe the arrest of development was rarely so 

 induced, for I took great pains to handle all cocoons with extreme 

 gentleness and, as we see from the third column of Table II, the 

 average number of unhatched eggs to a cocoon varies with the dif- 

 ferent mothers which would not be the case were it due to acci- 

 dent. Probably, therefore, infertility of eggs is due to lack of 

 fertilization; and indeed the frequent happening of the last cocoons 

 of a series proving most infertile is to be ascribed to the supply 

 of spermatozoa becoming exhausted. To test whether normal 

 parthenogenesis occurs I raised two immature females to maturity 

 without benefit of males; one moulted in March and the other in 

 April, which brought them to the mature condition with fully 

 formed epigyna, and both were allowed to live, with good feeding, 

 until August 30. One of them laid no eggs at all; the other made 

 a cocoon containing a few infertile eggs on June 18, and on June 

 26 dropped on the floor of the cage, without constructing a cocoon, 

 a mass of eggs that also proved infertile. These two individuals 

 had not been impregnated, and all the eggs laid by them were 



