OF GENERATION. 331 



in Mclolontha and in Mcloe, whereas in those which are rapidly con- 

 nected (Ephemera, Libellula, Musca), it is wholly wanting. 



But Hunter's * experiment proves that this appendage absolutely 

 contains semen, for by the application of the fluid contained in it, he 

 made the eggs of an unimpregnated female fruitful. Spallanzani f made 

 the same experiment, but with sperm from the male vesica seminalis, 

 and he also succeeded ; but Malpighi |., who made a similar one, was 

 unsuccessful, for he observed no development of the eggs. According 

 to Meinecke , this vesicle is empty prior to copulation, and after the 

 laying of the eggs, but between these two periods, it is filled with a 

 viscous fluid. 



If the semen be really received in this reservoir, we may ask, how 

 does impregnation ensue here as well as in those instances in which 

 the vesicle is wholly wanting ? We must have recourse to mere con- 

 jecture, for we have no positive observation upon the subject. It is the 

 usual opinion that the egg is rendered fruitful when it glides past the 

 aperture of the vesica seminalis, by the sperm suddenly falling upon it, 

 but this is contradicted by the observation that the development of the 

 egg commences even at the end of the oviduct, and that it has already 

 acquired a hard horny shell when it passes the vesica seminalis. Nor 

 does the conjecture explain the mode of fructification in those cases in 

 which that appendage is wanting. Opinions which have been pro- 

 pounded to explain it in the higher animals, for example, the theory of 

 absorption, whereby the sperm is conveyed through the blood to the 

 ovaries, cannot be applied to insects, which are totally deficient in 

 blood-vessels and absorbents. A third theory of generation maintains 

 the passage of the semen into the oviducts, which Suckow || states to 

 have positively observed. This opinion is not contradicted by the 

 distance of the oviducts, which, in many instances, is but trifling. 

 Consequently these oviducts are not analogous to the ovaries of the 

 superior animals, but to the tubes, the superior end of which only is 

 the ovary, whereas its lower end is the uterus, for, as Miiller has 

 informed us, the development of the germen already commences there. 



* Lectures 011 Comparative Anatomy, vol. iii. p. 370. 



J- Versuch liber die Erzeugung. PI. I. p. 245, &c. 



t Opera Omnia. vol. ii. De Bombycc. p. 41. (Lttgd. Batav. 1687. 4to.) 



Naturforschcr. 4 St. p. 115, &c. 



|| Heusingcr Zeitschr. f. d. Org. Pbys. vol. ii. p. 262. 



