METAZOA INSECTA. 493 



In the transformation from larva to pupa most of the 

 larval organs are destroyed, while from the so called "im- 

 aginal buds" that persist the parts of the pupa and imago 

 arise. The pupa transforms in a puparium, and emerges 

 in this entire group (Cyclorhapha) through an opening at 

 the anterior end which is provided with a lid. The de- 

 velopment is accelerated requiring from ten to fourteen 

 days only, and according to Weismann this metamorphosis 

 of the Muscidae is far more complex than in other insects. 



The adult Musca (No. 1262) is also more reduced than 

 the adult Tabanus. The mandibles and first pair of 

 maxillae have become useless and the mouth parts have 

 only one function, that of lapping. That this function 

 is performed with admirable perfection is demonstrated 

 whenever Musca is watched sipping its meal of sweetened 

 water. 



The parasitic Diptera the Pupipara are reduced to 

 the extremest degree. The wings have not only become 

 tiny scales as in the semi-parasitic flea, Pulex, but in the 

 Pupipara both wings and balancers are wanting altogether, 

 as seen in Melophagiis ovinus Linn. (PI. 1263, fig. i) and 

 Braula coeca Nitzsch (fig. 2). With this reduction of the 

 wings the thoracic segments have lost their typical fea- 

 tures and in Braula have become like those of the abdo- 

 men (see fig. 2). But this is not all. The remarkable 

 discovery by Adensamer of the bee parasite, Ascodipteron 

 (PI. 1264, A.phyUorhinae, dorsal view), proves that among 

 insects the law of specialization by reduction may obliter- 

 ate all trace of segmentation. In this parasite there is no 

 external head and only the structure of the internal organs 

 places it near Melophagus. 



The Pupipara develop by a process that is remotely 

 comparable to that of vertebrates. The young are re- 

 tained in an enlargement of the oviduct and are nourished 

 by a milk-like secretion. The larval stage is nearly or 

 wholly passed within the body of the parent so that the 

 young are born as -pupae a unique illustration of the 

 law of acceleration in development. 



