30G THE PRINCIPLES OF [Part II. 



liim, the males to tlic females were as six to one ; while exactly 

 the reverse occurred with the mature insects of the same species 

 caught in the fields. "With the iN europtera, Mr. "Walsh states that 

 in many, but by no means in all, the species of the Odonatous 

 groups (Ephemerina), there is a great overplus of males ; in the 

 genus Hctfcrina, also, the males are generally at least four times 

 as numerous as the females. In certain species in the genus 

 Gomphus the males are equally numerous, while in two other 

 species the females are twice or thrice as numerous as the males. ■ 

 In some European species of Psocus thousands of females may be 

 collected without a single male, while with other species of the 

 same genus both sexes are common." In England, Mr. Mac- 

 Lachlan has captured hundreds of the female Ax>atania muUebris, 

 but has never seen the male ; and of Boreus hyemalis only four 

 or five males have been hero seen.'" With most of these species 

 (excepting, as I have heard, with the Tenlhredinai), there is no 

 reason to suppose that the females are subject to parthenogene- 

 sis ; and thus we see how ignorant Ave are on the causes of the 

 apparent discrepancy in the proportional numbers of the two 

 sexes. 



In the other Classes of the Articulata I have been able to col- 

 lect still less information. "Witli Spiders, Mr. Blackwall, who has 

 carefully attended to this class during many years, writes to mo 

 that the males, from their more erratic habits, are more com- 

 monly seen, and therefore appear to be the more numerous. 

 This is actually the case with a few species ; but he mentions 

 several species in six genera, in which the females appear to bo 

 much more numerous than the males.^' The small size of the 

 males in comparison with the females, which is sometimes car- 

 ried to an extreme degree, and their widely-different appearance, 

 may account in some instances for their rarity in collections.''* 



*'*' ' Observations on N. American Xeuroptera,' by II. Hagan and B. D. 

 Walsh, 'Proc. Ent. Soc. Philadelphia,' Oct. 18C3, pp. 1G8, 223, 239. 



"> 'Proc. Ent. Soc. London,' Feb. 17, 1808. 



■" Another great authority in this class, Prof. ThorcU of Upsala (' On 

 European Spiders,' 1869-'70, part i. p. 205) speaks as if female spiders 

 were generally commoner than the males. 



'- See, on this subject, Mr. Pickard-Cambridge, as quoted in ' Quar- 

 terly Journal of Science,' 1808, p. 120. 



