438 Thos. H. Montgomery, Jr. 



represent these differences as clearly as the rounded originals do. 

 Now these are like the form and size differences of the abdomina 

 of the adults; the adult female has the more arched abdomen with 

 the pedicel placed further back, while the male has the narrower 

 and flatter abdomen with the pedicel situated further forward. 

 Therefore I conclude, and no reasonable objection can be enter- 

 tained to this opinion, that those spiderlings most resembling in these 

 particulars the adult females are females, and those most similar 

 to the adult males are males. And it will be recalled that inter- 

 mediate individuals are not found, and one can separate rapidly 

 and unhesitatingly the spiderlings from a given cocoon into two 

 lots. 



I had hoped to be able to distinguish the sexes at a still earlier 

 stage of growth, by constant differences in egg sizes, and for this 

 purpose preserved the eggs (all at the age of about twenty-four 

 hours) of the cocoon series of five different spiders. But this 

 expectation was not realized. The eggs in any cocoon differ 

 somewhat in volume, not greatly, but these size differences form 

 a graduated series and not two unbridgable groups. The sexual 

 differences of the hatched spiderlings being constant only with 

 regard to form but not always with regard to size of the abdomen 

 explains why we do not find female eggs always larger and so dis- 

 tinguishable from male eggs. 



The following table represents the proportions of the sexes 

 in those cocoons of which the young were preserved shortly after 

 hatching. The first column gives the number of the mother and 

 the letters designating her successive cocoons. The second gives 

 the day of oviposition, and the third the time interval between 

 oviposition and hatching. The succeeding columns state the 

 number of unhatched eggs, of males, of females, and the male 

 ratio: under the male ratio I understand the quotient obtained 

 by dividing the number of males by the number of females. 



