PROPORTION OF THE SEXES. 287 



easily escape observation tLan the other. Thus his brother Fritz 

 Miiller has noticed in Brazil that the two sexes of the same species of 

 bee sometimes frequent different kinds of flowers. With respect to 

 the Orthoptera, 1 know hardly anything about the relative number of 

 the sexes; Korte,* however, says that out of 500 locusts which he 

 examined, the males were to the females as 5 to 6. With the 

 Neuroptera, Mr. Walsh states that in many, but by no means in all 

 the species of the Odonatous group, 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 in excess, 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, f In England, Mr. MacLachlan has captured 

 hundreds of the female Apatania muliebris, but has never seen the 

 male; and of Boreus hyemalis only four or five males have been seen 

 here. J With most of these species (excepting the Tenthredinse) there 

 is at present no evidence that the females are subject to partheno- 

 genesis; and thus we see how ignorant we are of the causes of the 

 apparent discrepancy in the proportion of the two sexes. 



In the other classes of the Articulata I have been able to collect 

 still less information. With spiders, Mr. Blackwall, who has care- 

 fully attended to this class during many years, writes to me that the 

 males from their more erratic habits are more commonly seen, and 

 therefore appear 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.g The 

 small size of the males in comparison with the females (a peculiarity 

 which is sometimes carried to an extreme degree), and their widely 

 different appearance, may account in some instances for their rarity 

 in collections, f 



Some of the lower Crustaceans are able to propagate their kind 

 sexually, and this will account for the extreme rarity of the males; 

 thus Von Siebold^ carefully examined no less than 13,000 specimens 

 of Apus from twenty-one localities, and among these he found only 

 319 males. With some other forms (as Tanais and Cypris), as Fritz 

 Miiller informs me, there is reason to believe that the males are much 

 shorter-lived than the females; and this would explain their scarcity, 

 supposing the two sexes to be at first equal in number. On the other 

 hand, Miiller has invariably taken far more males than females of 

 the DiastylidaB and of Cypridina on the shores of Brazil; thus with a 



* " Die Strich, Zug oder Wanderheuschrecke." 1828, p. 20. 



+ " Observations on North American Neuroptera," by II. Ha^en and B. D. 

 Walsh, " Proc. Ent. Soc, Philadelphia," Oct., IS&J, pp. 168, 223, 239. 



X " Proc. Ent. Soc, London," Feb. 17, 1868. 



Another ^"eat authority with respect to this class. Prof. Thorell, of Upsala 

 (" On European Spiders," 186S-1870, part i, p. 205), speaks as if female spiders 

 were jcenerally commoner than the males. 



II See, on this subject, :Mr. O. P. Cambridge, as quoted in " Quarterly Jour- 

 nal of Science," 1868. p. 429. 



^"Beitrage zur Parthenogenesis," p. 174. 



