THE STRUCTURE AND FUNCTION OF THE PROBOSCIS 53 



observers, and although the proboscis of the blow-fly has been 

 a favourite subject of study for many years no observations 

 appear to have been recorded which throw any light on the 

 means by which the filtration is effected. In order to ascertain 

 the mechanism by which the filtration is accomplished the writer 

 (Graham-Smith, 19 ii, p. 390) made a large number of dissections 

 of the proboscis of the blow-fly, and carried out experiments on 

 the living fly to test the degree of its efficiency. 



The following account is reproduced from his paper. 



(A) The anatomy of the distal end of the proboscis of 

 the blow-fly. 



The proboscis of the blow-fly has been carefull}^ described 

 by Lowne (1895) and others, and consequently there is no 

 necessity to describe in detail the principal parts of the structure. 



Briefly the proboscis of the blow-fly consists of two parts, a 

 proximal conical portion, the rostrum, and a distal half, the 

 proboscis proper, or haustellum, which bears the oral sucker. 

 The relationship of the structures, which compose the main 

 portions of this organ, may be seen by reference to PI. XII, 

 which represents a schematic longitudinal section through the 

 proboscis, constructed from drawings made from numerous dis- 

 sections and serial sections which were studied in order to 

 ascertain whether any valvular structures exist in the proboscis. 

 These observations failed to reveal any valve-like structures. 



EXPLANATION OF PLATE XII. 



The right lateral half of the proboscis of the blow- fly divided in the middle line, 

 and seen from the cut surface. The diagram has been reconstructed from dissections 

 and serial sections. The mouth, prepharyngeal tube and pharynx are shaded. 



I. (Esophagus. 1. Pharyngeal tube. 3. Salivary duct. 4. Fulcrum (with 

 pharyngeal muscles). 5. Salivary valve. 6. Apodeme of the labrum. 7. Hyoid 

 sclerite. 8. Flange at proximal end of ligula. 9. Cavity of prelabrum (passing up 

 to prepharyngeal tube). 10. Thyroid sclerite and contained muscles. 11. Paraphysis. 

 1-2. Ligula. 13. Hypoglossal sclerite. 14. Cavity of prelabrum. 15. Salivary 

 gland of oral disc. 16. Prestomal teeth and prestomal cavity. 17. Labellum 

 showing pseudo-trachcK, the anterior and posterior sets opening into common 

 collecting channels. The epifurca can be seen running downwards behind the pseudo- 

 trachese. 18. Lateral plate of discal sclerite with nodulus (black). 19. Anterior 

 portion of prelabrum with contained muscles. 



The smaller figures are transverse sections at A — A and B — B, and are numbered 

 as in the larger figure. (From Gra.ha.m-Siri\th,J^ozirttat 0/ Hygiene, 191 1, PI. iv.) 



