272 EEPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



The external parts consist of tlie ovipositor (Fig. 12, B, and Fig. 14), 

 which is formed of two pairs of spines (rliahrlites) adapted for boring 

 into the earth, and the egg-guide (Figs. 12 and 14, eg), a triangular flap, 

 guarding the under side of the opening of the oviduct. 



Organs of special sense. — It is difficult to explain many of the actions 

 of our migratory locust, from the fact that it is hard for us to appreci- 

 ate the mental powers, instincts, and general intelligence of insects. 

 That they have sufficient intellectual powers to enable them to main- 

 tain their existence may be regarded as an axiom. But insects differ 

 much in intelligence and also in the degree of perfection of the organs 

 of sense. The intelligence of insects depends, of course, largely on the 

 development of the organs of special sense. 



The sense of sight must be well developed in the locust, there being 

 two large, well-developed compound eyes, and three simple ones (ocelli) 

 situated between the former, supplied with nerves of special sense. 



The antennse are, in the locust, organs of touch. The palpi are not 

 only organs of touch, but probably, as in some other insects, are en- 

 dowed with the sense of taste, enabling the locust to discriminate 

 between the different kinds of food, and select that best adapted to suit 

 its wants. It is possible that the labial nerves send branches of special 

 sense to the tongue, but this is a subject which has not been worked out 

 as regards the Acrydii, 



The ears are well developed in the locust, and we know that the sense 

 of hearing must be delicate, not only from the fact that a loud alarum 

 with kettles and pans affects them, but the movements of persons walk- 

 ing through the grass invariably disturb them. Besides this, they pro- 

 duce a fiddling or stridulating sound by rubbing their hind legs against 

 their folded wing-covers, and this noise is a sexual sound, heard and 

 appreciated by individuals of the other sex. Any insect which pro- 

 duces a sound must be supposed to have ears to hear the sound pro- 

 duced by others of its species. 



The ears (or auditory sacs) of the locust are situated, one on each side, 

 on the basal joint of the abdomen, just behind the first abdominal spira- 

 cle (Fig. 13). 



The apparatus consists of a tense membrane, the tympanum surrounded 

 by a horny ring. *' On the internal surface of this membrane are two 

 horny processes, to which is attached an extremely delicate vesicle filled 

 with a transparent fluid, and representing a membranous labyrinth. 

 This vesicle is in connection with an auditory nerve, which arises from 

 the third thoracic ganglion, forms a ganglion upon the tympanum, and 

 terminates in the immediate neighborhood of the labyrinth by a collec- 

 tion of cuneiform, staff-like bodies, with very finely-pointed extremities 

 (primitive nerve-fibres *?), which are surrounded by loosely aggregated 

 ganglionic globules." — (Siebold's Anatomy of the Invertebrates.) 



The following account of the histology of the digestive system of the 

 locust is appended. It has been prepared by Dr. Charles Sedgwick 

 Minot, of Boston, Mass. 



