THE HEAD OF THE BLOWFLY LARVA. 123 



able mistake, as they have no relations with the walls of the month. 

 M. Menzbier evidently thought that when retracted they lie in 

 the mouth. Such is, however, not the case ; they lie, as already 

 stated, in distinct cavities in the galea of the inaxilla?. 



The basal joint of the galea of the larva fly exhibits a very 

 remarkable structure. A series of radiating and dichotomously 

 dividing groves extends from the lateral margins of the mouth, 

 and covers a discoid area, occupying nearly the whole of the 

 under surface of the basal joint of the galea behind and outside 

 the sac, within which the hook lies. These tubes, although 

 without rings, bear a strong resemblance to the pseudotracheae of 

 the proboscis. The whole structure forms a suctorial disc, and is 

 at least analogous to the suctorial disc of the adult fly. The ter- 

 minal joint of the galea bears two sensory papilla? connected with 

 ganglionic sensory nerve terminations. Dr. Weismann regarded 

 them as the homologues of the antennas and maxillary palpi respec- 

 tively, an opinion which is clearly untenable if the organ is a galea, 

 and one which is likewise at variance with Dr. Weismann's own 

 observations on the development of the organs which 1 have 

 identified with the galea of the maxilla. 



In front of the mouth of the larva a strongly chitinised labrum 

 is present with a pair of thin membranous margins. Behind, the 

 orifice is bounded by the three-lobed labium already described. 



I am at present engaged in working out the development of the 

 proboscis of the adult fly, but I will indicate the conclusions to 

 which I think our present knowledge points, and which I expect to 

 be verified by further research. 



M. Kunkel de Herculais,* in his unfinished monograph on the 

 genus Volucella, states that the head of the flies is developed from 

 three pairs of " histoblasts," as he names the imaginal discs of 

 Weismann ; and so far as my present investigations have gone, I 

 think M. de Herculais is right. 



One pair form the optic and antennal discs of Weismann; these 

 are in relation with the cephalic or preaesophageal ganglion, and are 

 doubtless the modified procephalic lobes ; a second pair lie in the 

 basal joint of the galea, and a third appear to belong to the labium. 



The third pair, or labial discs, apparently coalesce around the 

 salivary duct, a fact known to Cuvier, who regarded them as the 

 representatives of the mandibles, and one which Dr. Weismann has 

 verified. 



* " Anatomie des Volucelles." Paris — in progress. 



