406 LECTURE xviri. 



setting seeds in the earth. In the saw-flies ( Tenthredo), the main 

 part of the ovipositor is long, slender, and serrated^ like the sting in 

 the bees. With this instrument the female saw-fly saws into the 

 substance of leaves, and there insinuates her eggs. The Ichneu- 

 mons have a similar apparatus, but extremely elongated and slender, 

 by means of which they introduce their ova beneath the skin of 

 other insects. 



Insects, like crustaceans, are occasionally subject to one-sided or 

 dimidiate hermaphroditism. Numerous instances of this kind are 

 given by Ochsenheimer.* In fourteen of the instances which he 

 cites, the right side was male and the left female ; in nine instances 

 it was the reverse. Occasionally hermaphrodites are found, where 

 the characters of one sex, instead of extending over one-half, are 

 limited to particular parts of the body, which agrees in the main with 

 the other sex. Thus an individual of the Gastrophaga Qiiercus has 

 been observed, in which the body, the antennae, and the left wings 

 were those of the female, the right wings those of the male. The 

 external sexual characters are very striking and various in the class 

 of insects, and readily lead to the detection of the hermaphroditical 

 condition of the internal organs. 



So far as regards the organic machinery for propagation, that 

 mechanism has reached its highest grade of complexity in the 

 class of insects. In the male individuals we have found " testes," 

 "epididymys," "vasa deferentia," "vesiculas seminales," "prostates," 

 " penis," and " claspers :" with a hundred-fold variety in the forms 

 and proportions of the several parts. In the female individual we 

 have seen, besides the ovaria and oviducts, special enlargements of 

 the latter, to which the name of " uterus " might be applied, 

 seeing that in certain insects the embryo was developed therein ; 

 and the vagina was complicated with a spermatheca, bursa copulatrix, 

 coUeteria, vulva, ovipositor, and copula. As might be expected from 

 the very common form of the ovaria, as long and slender tubes, they 

 offer peculiar facilities for observing the development of the ovum. 

 Professor Wagner f has ably availed himself of this peculiarity in 

 tracing out the progressive steps in its formation, and has given 

 good descriptions of the process, illustrated by figures of the parts, 

 in the female dragon-fly {Agrion virgo). The germs of the ova first 

 appear in the capillary beginning of the ovarian tube as a single file 

 of minute elliptical granules or nuclei : as the tube expands the cell- 

 wall appears surrounding the first part, and the ovum is now in the 



* CCLXI. t CCLXIL, p. 554, tf. 2. 



