SO ME PECULIARITIES IN REPRODUCTION. 333 



ness of females to the elimination of the disadvantageous^ 

 conspicuous in the course of natural selection. There may 

 be truth in both views, but both require to be supplemented 

 by the consideration, in part accepted by Wallace, that the 

 "secondary sexual characters" of both sexes are the natural 

 and necessary expressions of their respectively dominant 

 constitutions. 



The organs consist of :- 



MALE. 



The paired testes, usually formed 

 of many small tubes. 



Two ducts' (vasa deferentia) con- 

 ducting spermatozoa (perhaps 

 in part comparable to neph- 

 ridia). 



An unpaired terminal and ejaculn- 

 toryduct, paired and with two 

 apertures in Ephemerids only ; 

 sometimes formed by a union of 

 the vasa deferentia, sometimes 

 by an external invagination 

 meeting the vasa deferentia. 



I-Yom the vasa deferentia or from 

 the ejaculatory duct, opens a 

 paired or unpaired seminal 

 vesicle for spermatozoa. 



Various accessory glands, whose 

 secretion sometimes unites the 

 spermatozoa into packets or 

 spermatophores. 



Sometimes a copulatory penis. 



Often external hard pieces. 



FEMALE. 



The paired ovaries, usually formed 

 of many small tubes (ovarioles ).- 



Two ducts (oviducts) conducting 

 the ova (perhaps in part com- 

 parable to nephridia). 



An unpaired terminal region or 

 vagina, paired and with two 

 apertures in Ephemerids ; 

 usually formed from an ex- 

 ternal invagination meeting 

 the united ends of the oviducts. 



Near or from the vagina, opens 

 a receptaculum seminis for 

 storing spermatozoa received 

 from a male during copulation. 



Various accessory glands, e.g. those 

 which secrete the material sur- 



rounding the eggs. 



Sometimes a special bursa copula- 



trix in the vagina. 

 Often external hard 



ovipositor. 



pieces, e.g. 



Some peculiarities in reproduction. Many Insects, such as 

 aphides, silk-moth, and queen-bee, are exceedingly prolific. The 

 queen termite lays thousands of eggs, "at the rate of about sixty per 

 minute" ! 



The store of spermatozoa received by the female, and kept within the 

 receptaculum seminis, often lasts for a long time, for two or three 

 years in some queen-bees. Sir John Lubbock gives the remarkable 

 instance of an aged queen-ant, which laid fertile eggs thirteen years 

 after the last union with a male. 



Parthenogenesis, or the development of ova which are unfertilised, 

 occurs normally, for a variable number of generations, in two Lepidop- 

 tera and one beetle, in some coccus insects and aphides, and in certain 



