GEXERATION OF DfSECTS. 415 



formed into an ovarian sac and a generative medusa. The analogy 

 is beautifully and closely maintained throughout. 



The wingless larval aphides are not very locomotive ; they might 

 have been attached to one another by continuity of integument, and 

 each have been fixed to suck the juices from the part of the plant 

 where it was brought forth. The stem of the rose might have been 

 incrusted with a chain of such connected larvae as we see the stem of 

 a fucus incrusted with a chain of connected polypes, and only the last 

 developed winged males and oviparous females might have been set 

 free. The connecting medium might even have permitted a common 

 current of nutriment contributed to by each individual to circulate 

 through the whole compound body. But how little of anything 

 essential to the animal would be eflfected by cutting through this 

 hypothetical connecting and vascular integument and setting each 

 individual free ! If we perform this operation on the compound zoo- 

 phyte, the detached polype may live and continue its gemmiparous 

 reproduction. This is more certainly and constantly the result in 

 detaching one of the monadiform individuals which assists in com- 

 posing the seeming individual whole called "vol vox globator;" and 

 so, likewise, with the leaf-bud. And this liberation Nature has 

 actually performed for us in the case of the Aphis, and she thereby 

 plainly teaches us the true value or signification in morphology of 

 the connecting links that remain to attach together the different 

 gemmiparous individuals of the volvox, the zoophyte, and the 

 plant.* 



The phenomena of parthenogenesis have not been manifested in 

 any articulate animal of higher organisation than insects : they cease 

 at a lower grade of the parallel series of the molluscous invertebrata. 

 In some lepidopterous insects, which have been supposed to have the 

 faculty of producing fertile eggs without sexual intercourse, closer 

 observation has shown the mistake to have arisen from the unusual 

 circumstances under which the act of impregnation takes place. This 

 is the case with the moths of the genns'P^che, which the German 

 entomologists call "sac-trager" from the remarkable cases or sacs 

 which the larvae inhabit. The true state of the case has been ex- 

 plained by the observations of Yon Scheven and Siebold.f The 

 females of these moths never acquire wings, but develope their ova 

 under a grade of metamorphosis very little beyond that of the larval 

 state. The larvae which become females fabricate an entirely diff'erent 

 cocoon from that of the larvae which become males, and the sexes of 



* XXX. t CCLXIEL p. 93. 



