412 LECTURE xviir. 



primitive state amidst the various tissues w^hich the rest have con- 

 stituted in building up t'.ie body of the new animal may, by virtue 

 of their assimilative and fissiparous forces, lay the foundation of a 

 new organism."* 



The learned and ingenious authors of the deservedly popular 

 "Introduction to Entomology" admit it to be "an incontestible fact 

 that female Aphides have the faculty of giving birth to young ones 

 without having had any intercourse w^ith the other sex," and they 

 suppose "that one conjunction of the sexes suffices for the impreg- 

 nation of all the females that in a succession of generations spring 

 from that union." They adduce, in order to show that such a sup- 

 position is not contradictory to the general course of nature in the 

 production of animals, the case of the hive-bee, " in which a single 

 intei'course with the male fertilises all the eggs that are laid for the 

 space of two years ; " and the case of a common spider, showing 

 "that the sperm preserves its vivifying powers unimpaired for a 

 long-period, indeed a longer period than is requisite for the impreg- 

 nation of all the broods that a female Aphis can produce." But 

 these instances do not touch the question how one of such a brood, 

 insulated from all connection, should give birth to others. Admit- 

 ting that this phenomenon may depend on the inheritance of the 

 impregnating principle transmitted from generation to generation, 

 the problem for the natural philosopher to explain is, how this is 

 brought about. The superaddition of the " spermatheca" to the 

 vagina of the queen-bee, as of other oviparous insects, plainly ac- 

 counts for the fact in the economy of that insect which Messrs. 

 Kirby and Spence quote, according to the function of the part 

 determined by the well-devised experiments of Hunter on the silk- 

 moth. f To say that one conjunction of the sexes suffices to impreg- 

 nate the females of the successive generations of Aphides spring- 

 ing from that union, is little more than a statement of the fact ; 

 and it seems to have been so felt by the able entomologists cited, 

 who conclude their remarks by confessing — "It is, however, one 

 of the mysteries of the Creator that human intellect cannot fully 

 penetrate."! 



The completion of an embryonic or larval form by the develop- 

 ment of an ovarian germ-cell, as in the Aphis, without the immediate 

 reception of fresh spermatic force, has never been known to occur in 

 any vertebrate animal. 



♦ LXXXIV. p. 234. t CCXLVII. p. 175. 



X CCLI. vol. iv. p. 161. 



