266 DIPT ERA. 



observed, are without a distinct head, the forward part 

 of the body being membranous, as in the Syrphidae. 

 The observations of Weismann ^ upon the development 

 of the Muscidae throw light upon the subject of the 

 systematic position of the Diptera. He considers that 

 the metamorphosis of these flies is far more complex 

 than that of butterflies and other insects. During 

 their development nearly all the systems of internal 

 organs of the larva are destroyed, and out of their 

 remains the new organs of the imago are formed. This 

 last statement is not sustained by M. Ganin (see his 

 paper referred to below). The process is slow, as 

 the systems are not all destroyed at once. The dis- 

 integration is far less thorough in the butterflies than 

 in the Muscidae ; for in the former the muscles of the 

 abdomen are preserved, so that this part is capable of 

 motion, and the pupa does not for a single moment 

 cease to be a moving animal, while the life of the pupa 

 of the Muscidae is as absolutely latent as that of the 

 fertilized egg (p. 325). 



M. Ganin, after careful study of the post- embry- 

 onal development of insects, has arrived at the con- 

 clusion that the organization of the Muscidae has 

 undergone greater modification during its evolution 

 than that of other insects.- 



1 " Die nachembryonale Entwicklung der I^Iusciden nach 

 Beobachtungen an Musca vomitoria und Sarcophaga cai-naria,''^ 

 Zeit.f. Wiss. ZooL, Vol. XIV., p. 187, 1864. 



■^ See M. Ganin, " JNIaterials for a Knowledge of the Post- 

 Embryonal Development of Insects," Warsaw, 1876; extract in 

 American yahiralist, Vol. XI., 1877, p. 423. 



