1896.] -^^5 [Godrtard. 



On the Second Abdominal Segment in a Feio LibellulidcB. 



By Martha Freeman Goddard. 



{Read before the American Philosophical Society, October 2, 1S96) 



In the spring of 1892, I made, in connection with my work in the 

 zo51ogical department in Wellesley College, a somewhat careful study 

 of the second abdominal segment and the penis in a few male Libel- 

 lulinse. Though I was unable to do all that I had planned, it seems 

 worth while to publish my results in spite of their fragmentariness, 

 since they may serve as a basis for the work of some one else. 



I wished to learn the details of external structure in this part of the 

 body and to determine as far as possible the homologies of the various 

 parts. Tlie species studied were Diplax rubicundula and vicina ; Celi- 

 themis elisa ; Libellula pulchella, quadrupla and exusta ; Plathemis 

 trimaculata. I will begin by a full description of Diplax, rubicundula, 

 and then follow this by a brief statement of the more important respects 

 in which the other species studied ditfer from this one. 



The second abdominal segment, like most of the others, consists of a 

 narrow ventral piece, and a broad dorsal piece covering both back and 

 sides of abdomen. The first is the sternum; the second, the tergum. 

 The tergum (Fig. 1) is made up of three sclerites which form a longi- 

 tudinal series. The suture between the first and the second is present 

 only on the dorsal half of the segment, becoming obsolete as it ap- 

 proaches the sides ; that between the second and third is distinct for its 

 entire extent. Each side of the second sclerite is produced caudo- 

 laterally into a rounded process called the genital lobe («). The third 

 sclerite is shorter than either of the others ; it ends abruptly at the base 

 of genital lobe. The sternum {e, Fig. 2) consists of but one sclerite. 

 This is nearly as long as the first tergal one and lies ventrad of it, the 

 cephalic edge a little caudad of the cephalic edge of the tergum. The 

 cephalo-lateral angles are produced into wing-like processes (/) which 

 underlie the tergum and serve for the attachment of muscles. Caudad 

 of the sternum is a long extent of membrane which lies ventrad of the 

 caudal part of the tergum, and where it meets the sternum is so infolded 

 as to make a recess over which the latter projects like a pent-house roof. 

 Indeed, excejit at its very cephalic edge, the whole sternum bulges out 

 to a greater or less degree from the rest of the segment. 



On the membranous surface directly caudad of the sternum lie a pair 

 of stout appendages {(j) called hamules, readily to be seen with the 

 naked eyes. Each is a thick, laterally compressed and somewhat 

 elongated organ which is cleft distally into two divisions ; a short, strong 

 spur ending in an incurved, strongly chitinized tip (A), and a truncate 

 shorter portion {i) having the face turned towards the spur concave. 

 The liamule projects ventrad and the lobes lie cephalad and caudad ; the 



