Goddard.J ^^'O [Oct.?, 



truncate lobe is the more caudal. The divisions varj^ greatly in length 

 and shape in different species, though they generally form, as in Diplax 

 rubicuiulula, about one-third of the length of the entire appendage. 

 From the point of bifurcation, a ridge extends for a considerable distance 

 towards the base of the liamule. The mesal face of the organ is largely 

 membranous, especially at the base, so that the hamule can be flexed 

 freely towards its fellow of the opposite side. 



The hamules are borne by a chitinous framework {k). in shape 

 roughly resembling a U, and attached by its tips to the inner face of the 

 ventral sclerite. It seems to arise as a local chitinization of the mem- 

 brane which lies caudad of this sclerite. Projecting from either side of 

 the framework just caudad of the sclerite is a short rod (/«) to which is 

 attached one of the hamules. On the median part of the framework is 

 borne a triangle (Fig. 3, n). Its apex points cephalad ; its cephalo- 

 lateral sides are chitinized, though elsewhere it is membranous ; and its 

 base projects more or less caudad of the frramework. The basal angle of 

 either side forms a second, posterior point of attachment for the hamule 

 of that side. 



Another conspicuous structure is attached just caudad of the frame- 

 work on the median line (Fig. 2). When extended as in the diagram, 

 its tip points cephalad, but the distal end is ordinarily flexed upon the 

 proximal part. The organ consists of an enlarged basal portion, the 

 genital bladder, and of a slender, rodlike distal part, the penis. The 

 genital bladder is a somewhat hemispherical body. The caudal half of 

 its dorsal surface is attached for nearly its entire width to tlie under- 

 lying part of the abdomen and the rest of the dorsal face is chitinized. 

 The ventral face is imperfectly chitinized, the chitin being deposited in 

 three triangles ; a median caudal one {lo) and two cephalo-lateral ones 

 {o and r), all separated from one another by band-like membranous in- 

 terspaces, which, evidently, afford opportunity for variations in the size 

 of the bladder. This mode of attachment of the bladder causes the 

 structure of which it constitutes tlie base to appear as an appendage of 

 the second segment ; it does really, however, belong to the third, as is 

 clearly seen in OeUthemis elisa. 



The penis consists of three segments ; the first two are very simple, 

 but the third is extremely complicated. The first is chitinized continu- 

 ously on its dorsal surfiice, but the second, though in the main chitinous 

 on this aspect, is membranous on the dorso- mesal line. Both arc mem- 

 branous ventrally and this condition is evidently correlated with the 

 fact that in the position of rest this portion is covered bj' the reflexed 

 tip of the penis. What we have called the third segment consists of 

 two entirely distinct sclerites and of a cluster of appendages, some mem- 

 branous and some chitinous, borne at the extreme tip of the organ. The 

 lai'ger and more proximal sclerite (1) constitutes the dorsal aspect of the 

 segment. It is somewhat shield-shaped, but the distal angles are pro- 

 longed and curved around to the ventral side where thev almost meet. 



