128 [^une, 



remaining. Sunlight lias a strong effect on Stylo])idae other than 

 ^S(i/Iops itself in causing rapid emergence of the c5" • Thus I remember 

 one dull day in Brisbane coming across a number of Delphacid Homo- 

 ptera, which were heavily stylopized. At noon the sun came out 

 suddenly, and immediately the 6 Elenchi began to emerge from the 

 bodies of their hosts, w^hich were resting on the stems of some rushes. 

 I had several in the act of emergence at the same moment in full view. 



Actual pairing of the sexes has not been observed in the Stylopidae, 

 or at any i-ate the precise method of pairing is unknown. Smith and 

 Hamm think that pairing does not take place at all, and that the female 

 eggs cannot be fertilized owdng to the nature of the female reproductive 

 organs. Numerous observers have seen the d" Stylopid mount the host 

 in which the female is imbedded, and Mr. E. B. Nevinson has informed 

 me that he captured a bee with the 6 Stylops so attached (presumably 

 to the $ ) that it remained thus even in the killing bottle, and only 

 became separated on removing it from this. That the eggs of the 

 $ Sfi/IojJS can develop parthenogenetically is quite certain ; that they 

 always do so seems to me ver}"" unlikely. If it were the case of useless 

 males being produced in the case of only one species the fact would be 

 surprising, but it must be remembered that now the Strepsiptera have 

 been considered to consist of suj^erfamilies, families, and subfamilies, and 

 many genera, in all of which males are freely produced. In insects, 

 when the parthogenetic mode of reproduction becomes normal, the males 

 always appear to be lost entirely or only to be produced at intervals. 

 This ma}' happen in the case of very closel}'" allied species, the one being, 

 so far as is known, entirely parthenogenetic, no males being ever pro- 

 duced ; while its ally produces males and females in equal numbers, and 

 pairing betw^een these is regularly accomplished. That the Stylopidae 

 in their parthenogenesis resemble other insects I should infer from the 

 fact that in one species of Halictoxenus at least hundreds of females 

 have been obtained, but no 6 of the same species has ever been procured, 

 nor any bee containing a S puparium. It is clear that males are very 

 i-arely, if ever, developed in this case. There is no reason to doubt that 

 the developing eggs of Sti/lo]_:)s melitfae, as described in Smith and 

 Hamm's paper (Quart. Journ. Micr. Sci. 1914, p. 443), were developing 

 parthenogenetically. but I think it highly probable that it will be found 

 that sometimes the eggs are fertilized by the 6 ■ The " pick-axe " form 

 of the male aedeagus, almost universal throughout the Strepsiptera, is 

 so ver}^ remarkable as to suggest that it maj' be in some way adapted for 

 breaking up the tissues, so as to allow access to some of the ova of the 

 spermatozoa which are abundantly produced by the cS Stylops. 



