416 



ORGANS OF GENERATION. 



the eggs escaping by the anal passage ; but in 

 other cases, having joined that of the opposite 

 side, it terminates externally by a distinct 

 aperture ; near its extremity, however, it re- 

 ceives the auxiliary tubes or coeca, namely, 

 the spermotheca and the accessory glands. 



The spermotheca is a membranous saccu- 

 lus of varying size and shape, regarded by 

 Herold and Malpighi as a receptacle in 

 which the seminal fluid of the male is de- 

 posited and retained, an opinion which has 

 been sanctioned by subsequent anatomists ; it 

 is found only in such insects as deposit their 

 eggs in slow succession, and is presumed to 

 be a provision for the gradual fertilization of 

 the ova during their transit through the ovi- 

 duct. It is only upon this supposition that it 

 is possible to account for the impregnation of 

 some insects which are employed for a long 

 period in the business of oviposition, as is the 

 case, for instance, with the hive-bee, in which a 

 single coitus fertilizes all the eggs that are laid 

 for a space of two years, amounting some- 

 times to twenty or thirty thousand in number ; 

 and yet, in this case, it is difficult to conceive 

 how so small a reservoir, scarcely larger in- 

 deed than the head of a pin, can retain a 

 sufficiency of this fluid for such a purpose, a 

 difficulty which is scarcely lessened by admit- 

 ting the hypothesis of Dr. Ilaighton, who refers 

 the act of impregnation ralher to some pene- 

 trating effluvium or aura seminalis, which the 

 seminal liquor may emit during a long period, 

 than to actual contact between the semen arid 

 the ova. 



The auxiliary glands (glandule succentu- 

 riatte), which are appended to the oviduct of 

 insects, perform an office which is by no means 

 satisfactorily determined; the most usual sup- 

 position is that they furnish some secretion 

 connected with the investment of the ova, 

 either for the completion of the shell, or, as is 

 more probably the case, for the purpose of 

 uniting them together by a tenacious mucus 

 into the long strings or masses in which they 

 are not unfrequently extruded. The structure 

 of these secerning ccjeca differs in different 

 insects, but will be found to conform in most 

 cases to one or other of the following types ; 



1. Most frequently they are merely elon- 

 gated tubes closed at one extremity while the 

 other opens into the oviduct. 



2. In some cases the primary cceca give off 

 secondary branches. 



3. In others, as in ffippobotca, they are 

 ramified tubes terminated by blind canals. 



4. In Etater Murinus they present a very 

 remarkable structure, being composed of a 

 number of triangular capsules united by canals 

 arising from each angle until the terminal vessels 

 are reduced to simple cceca. 



The ovipositor is the last part of the female 

 generative apparatus of insects which we have 

 to notice. This singular appendage to the 

 oviduct presents many varieties in its structure, 

 being adapted to the introduction of the ova into 

 certain localities either fitted for their matu- 

 ration, or, as is more frequently the case, 

 suited to the necessities of the larva after its 



escape from the egg ; but a detailed account 

 of the forms which this organ assumes in dif- 

 ferent tribes would necessarily be incompatible 

 with the limits of this article, and the reader is 

 therefore referred for further information to the 

 article INSECTA. 



Some insects are ovo-viviparous in a mo- 

 dified sense, and their offspring are produced 

 in the larva or even in the pupa state, the eggs 

 being hatched in the body of the parent, and 

 the young matured to a certain extent before 

 they are expelled. In such cases the oviducts 

 unite to form a capacious matrix, in which at 

 certain seasons the larvae are contained either 

 agglomerated in masses, or arranged parallel 

 with each other in flat bands. In this state 

 each larva is invested in a delicate membra- 

 nous bag. It is remarkable that all these larvae 

 are carnivorous, their office being to remove 

 putrifying flesh ; hence the necessity of their 

 being produced in such a state as immediately 

 to commence the work to which they are des- 

 tined. 



Some Aphides, or plant-lice, are ovo-vivi- 

 parous in the early part of the year, but ovi- 

 parous as winter approaches, a provision evi- 

 dently intended to secure the preservation of 

 the embryo during the inclement season, the 

 eggs remaining unhatched until the return of 

 spring. 



The Aphides likewise in their mode of gene- 

 ration furnish the physiologist with one of the 

 most extraordinary anomalies met with in the 

 animal kingdom. From an accurate series of 

 observations, first instituted by Bonnet, and 

 subsequently confirmed by the indefatigable 

 Lyonnet, it is now received as an established 

 fact that the females of these insects have the 

 faculty of giving birth to young ones without 

 having had any intercourse with the other sex. 

 From the experiments of these naturalists it 

 appears to have been incontestably proved that 

 if a female Aphis at the moment of its birth 

 be rigorously kept from communication with 

 others of its species, it will, if supplied with 

 proper food, give birth to a brood of young 

 ones, and not only so, but if one of the off- 

 spring so produced be similarly treated, it like- 

 wise will prove fruitful, and so on to the fifth 

 generation, according to Bonnet, or even still 

 further, as Lyonnet afterwards ascertained. 

 Bonnet supposed, in explanation of this cir- 

 cumstance, that the Aphides are truly andro- 

 gynous, each being possessed both of ovige- 

 rous and impregnating organs ; yet this sup- 

 position is incompatible with the fact, that the 

 male insect is almost as common as the female, 

 and that the sexes copulate in the usual manner 

 during the termination of the summer season. 

 The only solution of this phenomenon appears 

 to be that one intercourse with the male suf- 

 fices for the impregnation of all the females 

 which in one season spring from the same 

 union. But the Aphides are not the only ex- 

 amples of this curious fact, as some of the 

 Branchiopod Crustaceans, as Daphnia pennata, 

 Mull. (Monoculus pulex, L.) are equally ca- 

 pable of producing fertile females through 

 several successive generations; nevertheless 



