SO 6 THE PRINCIPLES OP [Part II. 



him, the males to the 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 Neuroptera, Mr. Walsh states that 

 in many, hut hy no means in all, the species of the Odonatous 

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

 genus Hetaerina, 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 he 

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

 same genus both sexes are common. 69 In England, Mr. Mac- 

 Lachlan has captured hundreds of the female Apatania muliebris, 

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

 or five males have been here seen. 70 With most of these species 

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

 reason to suppose that the females are subject to parthenogene- 

 sis ; and thus we see how ignorant we 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. With Spiders, Mr. Blackwall, who has 

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

 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 be 

 much more numerous than the males. 71 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. 73 



M ' Observations on N. American Neuroptera,' by H. Hagan and B. D. 

 Walsh, 'Proc. Ent. Soc. Philadelphia,' Oct. 1863, pp. 168, 223, 239. 



70 Proc. Ent, Soc. London,' Feb. 17, 1868. 



71 Another great authoi-ity in this class, Prof. Thorell of Upsala (' On 

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

 were generally commoner than the males. 



12 See, on this subject, Mr. Pickard-Cambridge, as quoted in ' Qua*, 

 terly Journal of Science,' 1868, p. 429. 



Q 



