250 DIPT ERA. 



Latreille maintained that in Hymenoptera with peduncu- 

 lated abdomens the first abdominal ring was transferred to 

 the thorax, forming the posterior part of that region, and 

 concluded, therefore, that the peduncle was the second 

 abdominal ring. He also thought that a similarity existed 

 between the thorax of Hymenoptera and Diptera, main- 

 taining that in the latter also the first abdominal segment 

 joined the thorax. He, however, refused to accept the 

 view that the balancers represented the second pair of 

 wings. His theory in regard to the structure of the hy- 

 menopterous thorax is now generally accepted, but the 

 burden of evidence concerning the dipterous thorax is in 

 favor of Reinhard,! Weismann,^ and Hammond, ^ who 

 maintain that it is made of three rings only. Dr. Weis- 

 mann while holding this view says, in speaking of the 

 abdominal rings in the pupae of Muscidae, "At first the 

 foremost of these — the fifth ^ larval segment — encloses 

 the posterior part of the newly formed thorax, so that the 

 latter in a certain way grows out of \V (p. 254); and 

 again (p. 316), " On the third day the three segments of 

 the thorax form together a small ring which towards the 

 hinder part has joined the edge of the fifth segment of the 

 larva.'' Dr. Palmen^ opposes the view that the thorax is 

 made of three rings, asserting that in Corethra it is formed 

 of four segments, which he believes to be the case, more 

 or less, in all Diptera. Exhaustive investigations on the 

 anatomy of adults and the development of the larvae and 

 pupae are needed, as pointed out by Gosch, to settle this 

 question. 



1 Berliner Enioinologische Zcitschrift, Vol. IX., 1865, 2fl to 

 4th quarter. 



2 Zeits. f. wiss. Zoo/., 1864, 1866. 



3 Journal Linn. Soc, Vol. XV., 1880-81. 



* The fifth segment when the head is counted as one ring, but 

 the eighth when it is held to be made of four segments. 

 ^ Zur Alorphologie des Tracheensysietfis, 1877. 



