404 THE ALIMENTARY CAXAL Or THE IMAGO. 



insects examine their food with the maxillary palpi, and I ha\v 

 frequently seen the palps immersed in a drop of regurgitated 

 fluid, when the proboscis is withdrawn into the head capsule. 

 Near the extremity of the palpus there are always a number of 

 transparent spots, which appear as perforations. I have been 

 unable to obtain a section showing these as openings in the 

 cuticle ; beneath each there is what appears to be a tricho- 

 genic cell surrounded by nerve-cells. These perforations have 

 been described as pores, and it has been supposed that they 

 permit sapid fluids to come into contact with the nerve-end 



organs. 



The pharynx contains two rows of fine setae, which arc 

 undoubtedly connected with nerve - terminals. These are 

 situated on the epipharyngeal plate, one row on either side of 

 the median raphe. The extremities of these setae are directed 

 backwards towards the oesophagus. 



f. The Salivary Glands. 



In the imago of many insects two very distinct forms of 

 salivary glands are frequently present in the same individual, 

 besides one or more pairs of small accessory glands the 

 tubular sericterial glands, lingual glands, which either form, as 

 in Blatta and the larva of Musca, large thin-walled sacs, or, as 

 in the imago of Musca, long convoluted tubes ; and a pair of 

 racemose glands, the ducts of which join the ducts of the 

 lingual glands. In Volucella and the Syrphidae, and probably 

 in all pollen-feeding Diptera, as well as in the Hymenoptera, 

 the racemose glands are largely developed ; whilst in the 

 Muscidae they are absent, and only the tubular sericterial glands 

 are present. The latter arc just as well developed in the 

 Syrphid.-c which possess racemose glands, as in the Muscidae; 

 hence we cannot regard them as modifications of one and the 

 same organ. Neither can I hold that the large sac-like glands 

 in Blatta are mere salivary reservoirs, as is usually held. I 

 must regard them as sericterial and homologous with the 

 tubular form of gland which co-exists with the racemose glands 

 in so many of the Insecta. 



