404 LECTURE XVIII. 



more than eight eggs are laid. Near the outlet of the vagina are 

 two short caeca with thick walls, which contain a colourless, oil-like 

 mass. A little before these the spermatheca opens ; it is a colour- 

 less piriform appendix to the vagina, and is of so delicate a struc- 

 ture as to be readily overlooked when it is empty, but it is filled 

 with the spermatozoa after the coitus. The spermatheca is not so 

 crowded as in many other insects with the spermatozoa, and hence 

 their marvellous vibratory and undulatory movements may be wit- 

 nessed. 



The ova are fertilised during their passage along the vagina by 

 the spermatozoa, and are smeared with the viscous secretion of the 

 " colleteria," called glandes sebifiques by Leon Dufour. From the 

 different organisation of the internal generative organs of the ovi- 

 parous and viviparous female Aphides, it follows that the first cannot 

 ever bring forth living young ; and that when once this oviparous 

 generation is produced, no external circumstances, e. g,, warmth, 

 can convert the individuals of such generation into viviparous 

 iiemales. 



The males are frequently seen in coitu with the oviparous females, 

 and the embrace is so close, that when seized by his wings the female 

 is raised along with him. The males seem to be much fewer in num- 

 ber than the oviparous females ; yet Siebold * detected in all that he 

 examined spermatozoa in the spermatheca, and thence concludes that 

 the Aphides are polygamous ; to which the structure of the male 

 organs offers no physical impediment, as in Lepidoptera and Cole- 

 optera. 



In the Cicada the oviducts divide into several branches, on the ex- 

 tremity of each of which is a tuft of ovarian tubes. The spermatheca 

 consists of two small caeca. In the GeocoriscB the spermatheca is a 

 single long and flexuous caecum : in the Pentatoma it is pyriform, 

 and sometimes dilates into a second vesicle. 



In all Neuroptera the ovaries consist of multilocular tubes. In 

 the Ant-lion the spermatheca is a long, pedunculated sac : it is com- 

 plicated in the Phryganidce with a long tortuous tube ; and at the 

 base of the canal of communication there is a second flexuous tube, 

 and a short pedunculated *' bursa copulatrix." 



The proportion of the genital organs to the rest of the body in the 

 female Termites (Prep. No. 3147) is analogous to that in the male 

 LerncBa. 



In the Orthoptera, the ovarian tubes are commonly numerous and 



* CCLX. p. 308. 



