INSECTA. 229 



simple tubular form ; in the Meloe it is a vesicle furnished with a short 

 neck ; it is a large ovate bladder in most of the Lepidoptera, as in 

 Jig. 103. In the stag-beetle there are two mucous vesicles, the short 

 ducts of which unite into a common tube. In the Elater murinus 

 the colleterium bifurcates repeatedly, and the base of each fork dis- 

 tends into a triangular bag. 



Accessory filamentary tubes are met with in several of the butter- 

 flies. Certain social Hymenoptera, which, as John Hunter quaintly 

 observes, " have property to defend," possess a peculiar poison appa- 

 ratus, which is essentially a modification of accessory parts of the 

 female organs, and the only part which reaches its functional activity 

 in the neuters of the Bee and Wasp. The poison is secreted by two 

 long and slender ducts, which unite together and empty their secretion 

 into an oblong bag, which discharges itself by a narrow duct between 

 the valves of the sting. This is a long, slender, and sharp process, 

 with a serrated edge, which generally prevents its retraction when 

 thrust into the skin : the protecting valves are modifications of the 

 last abdominal segment. 



The corresponding parts are variously modified in other insects to 

 insure a proper deposition of the eggs. In some insects, as the Locusta 

 viridissima, the bivalve ovipositor is longer than the body, and by 

 means of it, the ova are conveyed to the proper depth in the soil, the 

 act of oviposition being precisely analogous to that of setting seeds in 

 the earth. In the saw-flies, a third organ, analogous to the sting in 

 bees, and similarly serrated, is superadded to the ovipositor : with this 

 instrument the female saw-fly (Tenthredo) saws into the substance of 

 leaves, and there insinuates her eggs. The Ichneumons 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 above cited instances, 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 Quercus 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. 



The development of an insect commences, as in all other animals, 

 from a. minute pellucid vesicle, having a central nucleus or spot, 



