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THE PROBOSCIS OF THE BLOW-FLY, CALLIPHORA 

 ERYTHROCEPHALA, MG.-A STUDY IN EVOLUTION. 



By W. Wesche, F.E.M.S. 

 (Read June 19th, 1908.) 



Plates 22 and 23. 



The proboscis of the Blow-fly is an object familiar to every 

 microscopist, and I venture to suggest that it is not only a 

 test for objectives, but also an equally critical test of powers 

 of observation. I have met many persons who possessed pre- 

 parations of this object, and were under the impression that 

 they were familiar with its structure ; but, as a matter of fact, 

 they were unacquainted with many of its most interesting 

 details, never gave a thought to the uses of the various parts, 

 and, as to the question of evolution, or how such an organ 

 came to be developed from portions of structure somewhat 

 similar to those which we now find present in the cockroach, 

 that was not even approached. 



Ever since there have been microscopes and microscopic 

 anatomists, the trophi of insects have been studied, and the 

 fact that all are modifications of an ancestral form was realised 

 by Savigny, one of the pioneers of his subject. It is quite 

 consistent with this, that, although the mouth of the Blow-fly 

 differs from the typical insect mouth in every detail, yet, with 

 the exception of one pair of palpi, all the parts can be 

 homologised with those of Periplaneta. The trophi in Diptera 

 may be separated from every other insect mouth, by the curious 

 tracheal and pseudo-tracheal structure. It is found developed 



