SOFT PARTS AND MECHANISM OF THE PROBOSCIS. 405 



The so-called salivary reservoir in Blatta is identical with the 

 larval sericterial gland of Musca in form and structure, and 

 this is replaced in the imago of Musca by the tubular lingual 

 gland ; whilst the lobulated glands of Blatta do not differ 

 from the racemose glands of Volucella and Syrphus, which co- 

 exist with a tubular lingual gland in the imago of these insects. 



In the imago of the Blow-fly two pairs of glands exist, which, 

 as they discharge their secretion either on the lips of the 

 proboscis, labial glands, or into the mouth, lingual glands, may 

 fairly be classed as salivary. 



Kraepelin describes a third pair which discharge their 

 secretion into the pharynx, but I have been unable to satisfy 

 myself that any such glands exist in Calliphora Erythrocephala; 

 they may be present, however, in some allied insects, such as 

 Lucilia and Sarcophaga. 



The Labial Glands (PL VI. and Fig. 31, sg) are situated at the 

 distal extremity of the haustellum, one on either side of the 

 poculum. The ducts of these glands run parallel with the 

 pseudo-tracheae, and terminate in nipple-like orifices between 

 them ; four or five of these are seen between each pair of 

 pseudo-tracheas (PL XXIII.)- 



Each gland consists of a sac lined by large columnar cells 

 with a distinctly rodded structure ; these cells are similar to 

 those of the sericterial (lingual) glands of the imago. I have 

 been unable to detect any cellular lining to their branching 

 ducts, which are usually distended with a coagulable fluid. 



Kraepelin believed that these glands open by short wide 

 ducts into the poculum, an opinion which I formerly held ; but 

 I have so frequently traced the ducts to the nipples between 

 the pseudo-tracheas that I can no longer agree with Kraepelin. 

 Further, Kraepelin regards these nipples as sensory organs, a 

 view which is not supported by any of my sections. I have 

 been quite unable to trace nerves to these papillae. 



The purpose of the labial glands is clearly to keep the surface 

 of the sucker moist with a tenacious viscid fluid \vhich differs 

 entirely from the clear watery secretion of the lingual glands. 



The Lingual Glands or Sericteria. These glands replace the 



