122 15. T. LOWNE ON THE STRUCTURE OF 



lobecl labium ; this and the ventral portion of the corresponding 

 segment is very apparent in the larva, and remains apparent until 

 the insect passes into the pupa stage. 



Before the escape of the larva from the egg the first pair of 

 maxilla} become parallel, and project beyond the bead. The pro- 

 cepbalic lobes disappear so far as tbe external structure of the 

 embryo is concerned, they become the antennal and optic discs of 

 Weismann, and, buried in the interior of tbe larva in relation with 

 the cephalic nerve-centre, remain rudimentary until tbe approacli 

 of tbe change of the larva into tbe pupa. Lastly, tbe cephalic 

 cap is reduced to a small triangular plate, which dips down between 

 the maxilla} and terminates in a point in front of the mouth, in 

 relation with the chitinised labrum. In the adult maggot the two 

 cylindrical maxillae are as recognizable as they are in tbe embryo, 

 or the newly hatched larva. Each is segmented transversely, so 

 that it consists of an ultimate and a basal portion, and exhibits 

 an unmistakable identity with a portion of the typical maxillae of 

 such insects as the cockroach. 



Such a typical maxilla consists of a basal joint, tbe cardo ; a 

 stalk, the stipes ; a blade, the lacinia or mando ; and a hood, the 

 galea. The galea further consists of two joints which form a 

 sheath over the lacinia. Lastly, a palpus, of two or more joints, is 

 supported by the stipes. 



I shall now proceed to show that the cylindrical organ, which I 

 have for brevity hitherto spoken of as the maxilla, represents only 

 a part of that organ, namely, the galea. Like the galea it consists 

 of two joints, and like the galea it forms a sheath for the lacinia or 

 mando. 



A careful examination of the blowfly larva shows that the great 

 lateral hooks lie in a cavity of the galea when retracted, exactly as 

 the lacinia of a typical insect is enclosed in the galea. On the other 

 hand the hooks are articulated with a distinct cardo, the H-shaped 

 piece of Weismann. The other parts of the maxilla, the stipes and 

 palpus, are, however, indistinguishable. 



M. Menzbier * severely criticises certain statements which I 



formerly made in my work on the blowfly, f and I admit that in 



some measure I laid myself open to his strictures, for I mistook the 



great hooks for the mandibles. M. Menzbier speaks of these hooks 



as chitinised thickenings in the walls of the mouth, a less excus- 



* " Bull. Soc. Imp. Nat. Moscow," T. 55. 



t " Anatomy and Physiology of the Blowfly," London, 1870. 



