Fig. 307.—Upper side of head and digestive canal of Myrmeleon larva: a, crop; b, “stomach”; c, free ends of two urinary tubes; c′, common origin of other six tubes; d, cœcum; e, spinneret; ff, muscles for protruding its sheath; gg, maxillary glands.—After Meinert, from Sharp.
In the larvæ of weevils (Calandra sommeri) there is a crop (Fig. 305), but not in the larva of Calosoma; also, according to Beauregard, in the pollen-eating beetles Zonitis, Sitaris, and Malabris it is wanting, while in Meloe it is highly developed (Kolbe).
The crop forms a lateral dilatation of the end of the œsophagus in the larvæ of weevils and of saw-flies (Athalia centifoliæ, Fig. 306).
The “sucking stomach” or food-reservoir.—This is a thin muscular pouch connected by a slender neck with the end of the œsophagus or the crop, when the latter is present. There is no such organ in Orthoptera, except in Gryllotalpa. It is wanting in the Odonata and in the Plectoptera (Ephemeridæ); in Platyptera (Perlidæ and Termitidæ), in Trichoptera, and in Mecoptera (Panorpidæ). In most adult Neuroptera (Myrmeleonidæ, Hemerobiidæ, and Sialidæ), but not in Rhaphidiidæ, the long œsophagus is dilated posteriorly into a kind of pouch or crop, and besides there is often a long “food-reservoir” arising on one of its sides, that of Myrmeleon (Fig. 307) and Hemerobius being on the right side.
Fig. 308.—Digestive canal of Sarcophaga carnaria: a, salivary gland; b, œsophagus; c, food reservoir; f-g, stomach; h, intestine; i, urinary tubes; k, rectum.—From Judeich and Nitsche.
A true food-reservoir is present in most Diptera (Fig. 308) as well as in the larvæ of the Muscidæ, but according to Dufour it is wanting in some Asilidæ and in Diptera pupipara, and according to Brauer in the Œstridæ. The food-reservoir in Diptera is always situated on the left side of the digestive canal; there is usually a long neck or canal, while the reservoir is either oval or more usually bilobed, and often each lobe is itself curiously lobed.
In Lepidoptera (Figs. 309, 310) the so-called “sucking stomach” is, as Graber has proved, simply a reservoir for the temporary reception of food; though generally found to contain nothing but air, Newport has observed that in flies it is filled with food after feeding. He has found this to be the case in the flesh fly, and in Eristalis he has found it “partially filled with yellow pollen from the flowers of the ragwort upon which the insect was captured,” the pollen grains also occurring in the canal leading to the bag, in the gullet, and in the stomach itself. Graber has further proved by feeding flies with a colored sweet fluid that this sac is only a food-receptacle. As he says: “It can be seen filling itself fuller and fuller with the colored fluid, the sac gradually distending until it occupies half the hind-body.”
The food-reservoir of the Hymenoptera is a lateral pouch at the end of the long, slender œsophagus, and has been seen in the bee to be filled with honey.
