260 NEW YORK STATE MUSEUM 
the supporting framework heretofore described. This is the 
sheath of one of the Libellulidae, Nannothemis. gq and r show 
the same type of sheath a little more chitinized and much more 
reflexed up and over the penis. s 
? >) is from Didymops and shows a 
eel A SE transitional condition between those 
P 7 uf S preceding and those following. 
Tere the sheath is flat but chiti- 
nized entirely and reflexed more 
over the penis. ¢ and u show the 
d u highest specialization of sheaths of 
Pg 26 this type—thick, chitinized, in- 
terior surface flattened, and much reflexed for the reception of the 
penis. ‘These were found among Aeschnidae. ‘These sheaths of 
Cordulegaster and Tachopteryx are stiff, hard, black structures. 
They are supported by the framework the same as that indi- 
cated at + for Nannothemis. | 
Figure 27 shows a more highly specialized type than in 
meorS AG, Wins ion Or Saeailn seams wO le Meter iniedl 
to fulfil its function than the former type and in fact each 
sheath here is a very concave, 
Oo IS hollow receptacle for the penis. 
p is the sheath of Gomphus, a 
very well chitinized structure 
with a fairly deep cavity for 
the reception of the penis, indt- 
cated by a cross-section of its 
deepest portion. wv indicates 
the position of the underlying 
BIE R27 framework. q is the sheath of 
Gomphaeschna, one of a slightly different form in that the 
cross-section of its deepest part presents a wedge-shaped cavity. 
The other letters 7, s and ¢ represent other forms constructed 
cn the same general plan as that of Gomphaeschna. 
In figure 28 the relative development of the hamules in the 
Anisoptera is shown, special attention being called to the de- 
velopment of the first or anterior hamule from the lamina. This 
is a series beginning with Cordulia shurtleffi and ending 
with Ophiogomphus. 
