400 LECTURE XVIII. 



to th6 coitus, and passes from the sperm reservoir into the vulva of 

 the female, which is retained in contact with the base of the male's 

 abdomen by the claspers attached to that part. 



The spermatozoa in all hexapod insects are filiform, and often re- 

 markable for their extreme length ; the anterior extremity is usually 

 thickened for a considerable extent. 



The sperm-cells usually contain many '* spermatoa," or vesicles of 

 development ; these spermatoa are at first transparent, then granular, 

 and lastly, the spermatozoon is developed, one in each. This makes 

 the spermatoon change its form : it is stretched by the uncoiling 

 of the spermatozoon, bursts and allows it to escape. Thus let 

 free in the common sperm-cell, the spermatozoa group themselves 

 into regular bundles. Sometimes these fasciculi resolve them- 

 selves, and the spermatozoa disperse as soon as the sperm-cell gives 

 way ; but usually a part of the sperm-cell remains as a partial 

 sheath to the bundle, and when the spermatozoa remain in this way 

 closely packed together, the whole bundle might be taken for a gigan- 

 tic spermatozoon. The bundle is very long, and appears convoluted 

 in a knot in Staphylimcs, but is resolvable into its constituent sper- 

 matozoa, which become separated as they advance along the sperm- 

 duct. But here frequently, by the addition of the prostatic secre- 

 tion, they are again collected into fresh bundles, and packed up 

 into " spermatophora." These secondary aggregates present an 

 elegant arrangement in the Locustince, being delicately barbed like 

 a feather, and the spermatophora, with their fertilising contents, 

 are finally conveyed in coitu to the proper " vesicula seminalis," or 

 " spermatheca," which, as in most other hexapod insects, belongs to 

 the female. 



As a general rule, the life of an insect soon ends after the great 

 act of impregnation has been fulfilled. The change of form prior to 

 the acquisition of the procreating power is usually extreme, and 

 rapidly undergone ; the ordinary every-day life of the insect, spent in 

 acquiring and consuming its daily food, forms a far larger proportion 

 of its existence, and is passed under a very different and a very in- 

 ferior form ; which, if in comparison to the last stage, we should 

 regard as the more typical form of the animal, we shall not probably 

 err. The cockchaffer passes three years as a subterranean worm, 

 but lives hardly as many weeks in its winged state. An ordinary 

 observer sees and knows the May-fly only in that liiet joyous stage of 

 its existence, and deems its life concentrated in one winged nuptial 

 holiday ; but this so-called Ephemera has previously passed three 

 hundred and more working days as an aquatic larva. 



In no class of animals are the parts of generation so complex as in 



