OVIPOSITORS OF INSECTS. C83 



a drop of fluid that has a peculiarly-irritating effect upon the Vege- 

 table tissues, occasioning the production of the ' Galls,' which are 

 new growths that serve not only to protect the larvae, but also to 

 afford them nutriment. The Oak is infested by several species of 

 these Insects, which deposit their eggs in different parts of its 

 fabric ; and some of the small ' Galls' which are often found upon 

 the surface of Oak-leaves, are extremely beautiful objects for the 

 lower powers of the Microscope. It is in the Tenthredinidce, or 

 Saw-flies, and in their allies the Siricidce, that the Ovipositor is 

 furnished with the most powerful apparatus for penetration ; and 

 some of these Insects can bore by its means into hard timber. 

 Their ' Saws ' are not unlike the ' Stings ' of Bees, &c. , but are 

 broader, are toothed for a greater length, and are made to slide 

 along a' firm piece that supports each blade, like the ' back' of a 

 Carpenter's 'tenon-saw;' they are worked alternately (one being 

 protruded while the other is drawn back) with great rapidity ; and 

 when the perforation has been made, the two blades are separated 

 enough to allow the passage of the eggs between them. — Many 

 other Insects, especially of the order Diptera, have very prolonged 

 Ovipositors, by means of which they can insert their eggs into the 

 Integuments of Animals, or into other situations in which the 

 Larvae will obtain appropriate nutriment ; a remarkable example 

 of this is furnished by the Gad-fly (Tabanus), whose Ovipositor is 

 composed of several joints, capable of being drawn-together or 

 extended like those of a Telescope, and is terminated by boring 

 instruments ; and the egg being conveyed by its means, not only 

 into but through the integument of the Ox, so as to be imbedded 

 in the tissue beneath, a peculiar kind of inflammation is set-up 

 there, which (as in the analogous case of the Gall-fly) forms a nidus 

 appropriate both to the protection and to the nutrition of the 

 Larva. Other Insects which deposit their eggs in the ground, such 

 as the Locusts, have their Ovipositors so shaped as to answer for 

 digging holes for their reception. — The preparations which serve to 

 display the foregoing parts, are best seen when mounted in Balsam; 

 save in the case of the Muscles and Poison -apparatus of the Sting, 

 which are better preserved in Fluid or in Medium. 



532. The Sexual organs of Insects furnish numerous objects of 

 extreme interest to the Anatomist and Physiologist ; but as an 

 account of them would be unsuitable to the present work, a refer- 

 ence to a copious source of information respecting one of their most 

 curious features, and to a list of the Species that afford good illus- 

 trations, must here suffice.* The Eggs of many Insects are objects 



* See the Memoirs of M. Lacaze-Duthiers ' Sur l'armure genitale des 

 Insectes,' in "Ann. des Sci. Nat." Ser. 3, Zool., Tomes xii., xiv., xvii., 

 xviii., xix. ; and M. Ch. Robin's "Memoir sur les Objets qui peuvent 

 etre conserves en Preparations Microscopiques " (Paris, 1856), which is 

 peculiarly full in the enumeration of the objects of interest afforded by 

 the Class of Insects. 



