178 Annals Entomological Society of America [Vol. XIV, 
primitive pairs of appendages belong primarily to urites eight, nine, ten 
and eleven. 
The most varied names have been applied, not only to the group of 
structures (genitalia, hypopygia, genital apparats, armature genitale, 
armature copulatrix, geschlechtsanhange, terminalia, pygidia, etc.), but 
also to each of the several parts. But in spite of the elaborate protest 
of almost every author who has dealt with these parts, at the confusion 
of names and lack of any knowledge of the homology of the various 
parts exhibited in the work of their predecessors; and in spite of several 
recent ambitious attempts to homologize the structures in all the orders 
of insects the problem remains today much as in the past. Each 
worker must select such names as are evidently appropriate for applica- 
tion to as many as possible of the structures that he finds; and, when 
this is done, must still devise names of his own for convenience of 
handling many other parts, the homology of which with other groups is 
absolutely unknown. The fact is that the variations of these parts in 
the orders of insects is so unlimited; and so relatively little detailed 
study of the conditions in various families has been completed; that 
the time is not ripe to attempt to construct an ancestral, hypothetical 
form from which the variations in the various groups can be derived, 
or even to say which of the parts in the groups described have had 
the same origin. Much as a more uniform nomenclature is to be 
desired, it seems to me that real, ultimate progress in this direction 
must await further isolated investigations, until we begin to com- 
prehend something of the range of variation in the orders. 
The posterior half of the abdomen of the males of the Syrphidz has 
been completely transformed (See Figs. A to N, Plate IX) and curiously 
modified for the support, protection and manipulation of the genitalia 
proper. This has resulted in dividing the abdomen sharply into two 
groups of segments; a caudal portion that is reduced in size and modified 
in shape or position or both, until it is quite distinct from the normal 
urites of the cephalic portion. I have found it convenient to designate 
these two divisions the preabdomen and the postabdomen. 
NUMBERING OF THE SEGMENTS. 
The following assumptions, in line with the conclusions of 
morphologists, but still assumptions, I believe, have been made in 
interpreting the identity of the segments in the postabdomen. 
(1) The anus opens primitively between the eleventh tergite and its 
corresponding sternite, though these sclerites may not be recognizable 
in the highly specialized insects. 
(2) The genital orifice is primitively between the ninth and tenth 
sternites, though the development of the penis may carry it to a point 
without any evident relation to the tenth urite. 
(3) There are never more than eight pairs of spiracles on the 
abdomen. 
(4) In the Diptera the style-bearing segment is the tenth. 
If these premises be sound, it is evident that a complete renumbering 
of the segments of the abdomen is called for. 
