INSECT A. 503 



appear to occur in two forms : (i) as vesicles containing some clear floating 

 globules, found only in some Diptera in the posterior region of the 

 abdomen in the larvae (Tabanus, &c.), or in the basal joint of the antennae 

 of the imago ; (2) as the chordotonal organs. The essential structure of 

 these organs consists of a nerve ending in a ganglion, the cells of which 

 are provided with terminal processes or end-organs, composed each of a 

 terminal rod (' Endstift ') variously conformed and inclosed within a sheath 

 or ' scolopophore.' The end-organs are either connected directly to the 

 hypodermis or indirectly by a lateral filament. They appear to occur 

 in the larva as well as the imago, and in all orders of Insecta except 

 Thysanoptera, where they have not been detected. They are found in 

 groups of 2-200 in various parts of the body, antennae, palpi, legs, wings, 

 in the halteres of Diptera, and upon the dorsal aspect of the abdomen. 

 Among the Orthoptera, they are connected in Acrididae with a thin 

 membrane, of which there are two, one on each side of the first abdominal 

 somite ; and in Locustidae and Gryllidae they lie in a special pit under 

 a thin membrane on each side of the proximal ends of the tibiae of the 

 fore limbs. The main trachea of the limb is dilated between the two 

 organs. Cells furnished with a pointed projecting rod, and connected 

 to a nerve, are found in various Insecta on the antennae, and on the palpi, 

 and in various parts of the oral cavity, e. g. in the Bee. In the first two 

 instances they are supposed to be olfactory, in the third gustatory in 

 function. 



Salivary glands, varying in shape, number, and structure, open into 

 the oral cavity, the most important pair belonging to the labium. They 

 appear to be developed close to the mandibles and not from the stomo- 

 daeum. Silk glands or serictaria open on the labium in the larvae of 

 Lepidoptera and the Tenthredinidae, &c. among Hymenoptera. They are 

 developed close to the inner side of the labial limbs. The oral cavity is 

 closed in the larvae of Dytiscus and of Megaloptera among Neuroptera 

 (e. g. Myrmeleo, Chrysopd) which suck up the juices of their prey through 

 the perforated mandibles, in the imago of Epheineridae and male Coccidae 

 and Aphidae. In the last-named family, the male and perfect female 

 Phylloxera are stated to want the digestive tract. The stomodaeum varies 

 in complexity. It may dilate into a crop and the muscular walls of its 

 posterior part become much thickened and the chitinous lining ridged 

 and toothed, forming a gizzard (Orthoptera, some Coleoptera, &c.). It may 

 be provided with a dilatation or so-called sucking stomach, attached by 



cones are fluid, and the style ( = rhabdome) of the four retinophoral cells does not expand into a 

 basal pedicel. This last-named structure is perhaps more or less characteristic of nocturnal Insecta. 

 The red light which is reflected outwards from it, is especially well seen in Moths. It is evident 

 that Grenacher's acone eyes in particular will require re-examination in the light of Patten's 

 researches. 



