Coddard.] -1^ [Oct. 2, 



haps corresponds to tlie hood of Diplax. Attached to the hase of this 

 structure on either side is a tiny, membranous, finger-lil^e lobe. The 

 tip of the penis is formed by a great mass of membrane which projects 

 from the distal end of the third sclerite described above. This mem- 

 brane is covered with scattered chitinized papillse and is chitinized in 

 such a way as to form a pair of irregularly shaped sclerites, somewhat 

 like a moose's antlers, narrow at the base, broadening distally and 

 uniting dorsally and ventrally so as to form a ring which divides the 

 membrane into a proximal and a distal division. This arrangement 

 will be made clear by a glance at the diagram (Fig. 14). At the base of 

 these sclerites on either side is a small piece visible after the removal of 

 the shield ; these pieces appear to be rudiments of structures much 

 more developed in L. quadruj)la. 



In L. quadrupla, the general appearance is much the same as in the 

 species last described ; there are, however, one or two interesting differ- 

 ences in the penis-tip. The hood is bi-lobed and so far as I could dis- 

 cover, there are no such lobes laterad of it as in L. pulchella. The mem- 

 branous tip of the penis is not chitinized in any part, but the chitinous 

 papillfE with which it is beset are much more closely placed in a region 

 which corresponds with that part which in L. pulchella'i?, chitinized. It 

 seems possible that this massing of papill* is, so to speak, an attempted 

 adaptation to certain unkown conditions and that the chitinization is a 

 more satisfactory adaptation to the same conditions. The dorsi-mesal 

 portion of the membrane is largely free from papillae and is extended 

 into a long, finger-like, membi'anous tip. 



Plathemis trimaculata is in several respects a most interesting species. 

 The first abdominal. segment bears on its ventral aspect a pair of chitin- 

 ous lobes ; these structures have a position on the first segment exactly 

 corresponding to that which the hanlules occupy on the second, and 

 their form is not unlike that of the undivided hamules found in many 

 kinds of Libellulinse. They are, however, continuous with the abdomi- 

 nal wall instead of being jointed to it as are the hamules. 



In the second segment, the sternum is short ; it bears on its free edge a 

 small median lobe which is indented on the mesalline so as to form two 

 scallops (Fig. 16). The hamules show only very slightditierentiation into 

 lobes. The cephalic lobe, Avhich corresponds to the spur of the ordi- 

 nary hamule, is shaped somewhat like a man's boot, the toe of the boot 

 being turned towards the caudal lobe. The toe alone is free, but from 

 the point of division between the two lobes a membranous band ex- 

 tends towards the base of the hamule ; if this membrane were unfolded 

 the condition found in the other Libellulinsie would be produced. The 

 caudal lobe is deeply grooved at its tip so that it appears almost bi- 

 lobed. I am unable to describe the penis. 



This species seems to me to give us some reason to believe that the 

 hamules are the survivors of the series of abdominal appendages jiresent 

 in the ancestor of the insects. And in this connection, I would suggest 



