26o NEW YORK STATE MUSEUM 



the supporting framework heretofore described. This is the 

 sheath of one of the LibelhiUdae, Nannothemis. q 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 

 transitional condition between those 

 preceding and those following. 

 Here the sheath is flat but chiti- 

 nized entirely and reflexed more 

 over the penis, t and u show the 

 highest specialization of sheaths of 

 ^^^- 2^ 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 X for Nannothemis. 



Figure 2y shows a more highly specialized type than in 

 figure 26. This form of sheath seems to be better fitted 

 to fulfil its function than the former type and in fact each 



sheath here is a very concave, 

 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, indi- 

 cated by a cross-section of its 

 deepest portion. x indicates 

 the position of the underlying 

 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 r, s and t represent other forms constructed 

 on 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. 



