Mouth-organs of the Diptera. 183 



Now with regard to my sins of omission. Mr. Waterliouse 

 is doubtful as to what I mean by parts of the maxilla ; yet on 

 page 154 of my book I have indicated that I regard the lancets 

 as homologous with the palpiger and the lacina respectively. 



My critic then makes it appear that " I blow hot and cold" 

 according to my necessities. It is true I said that the position 

 of tliepseudo-labium is no evidence from a morphological point 

 of view. In this Mr. Waterhouse concurs. But I have 

 nowhere stated that position is never of value in establishing 

 tlie morphology of a part. 



It is possible that two pairs of appendages are fused in the 

 dipterous proboscis ; it is conceivable that three are so united, 

 and it is further possible that these limbs are so entangled 

 and crossed, that position would afford no evidence of the 

 morphology of their distal extremities. Moreover the mere 

 similarity of a terminal joint to that of an homologous appen- 

 dage, such as Mr. Waterhouse appeals to, is not evidence that 

 this joint belongs to a mandible or a maxilla. The hoofs of 

 a horse's feet are similar ; but it would be hazardous to con- 

 clude that a limb with two hoofs consists of a fore and hind 

 limb united. I see no reason at all why the terminal joint of 

 one of the divisions of the maxilla should not resemble a 

 mandible when it has similar functions to perform. 



As regards the simple eye of the flea the case is very 

 different. Its relation to the antenna is such that it cannot 

 be explained on the supposition that the sternal plates of the 

 cephalic segments are dorsal, as the position of the antennee 

 is explained in Truxalis and Fulgora. Moreover Mr. Water- 

 house supposes an imaginary case, which does not exist so 

 far as we know. It will, I think, be time to consider its 

 bearings on the view I have adopted after its discovery. In 

 the meantime I assume that it does not happen that the 

 compound eye ever bears the relation to the antennas which 

 the simple eye of the flea exhibits. 



Mr. Waterhouse credits me with a consistency which I do not 

 deserve. When I published my book on the Blow- fly in 1870 I 

 never said of the proboscis that " it is mainly formed from the 

 maxillae." I then regarded it as a complex of several meta- 

 meres. I was wrong; but until I discovered the manner in 

 which it is developed no one had done so. The contradictory 

 statements of various writers on the subject will themselves 

 speak for the difiiculty which exists in making the parts of 

 the proboscis conform to the received theory ; and the very fact 

 that some have regarded it as composed of several meta- 

 meres whilst others deny it metameral characters shows that 

 the theory does not fit with the facts. 



