36 ENTOMOLOGICAL NEWS [Feb., '22 



fuk'a penis is inflated, Plate II, fig. 9. The lateral lobes in Plathcmis 

 are paddle-shaped and the medial lobes of incesta and jesscana are cov- 

 ered by a prominent chitinous hood, Plate II, fig. 10, and Plate III, fig. 

 26. In the composita series, including incesta, jesscana, etc., the various 

 soft lobes are very erectile and are covered with a plush of erectile 

 hairs. See Plate III, fig. 26. 



The homologies of these various lobes will be more apparent in the 

 figures of the second article where a larger series of species is figured. 



THE INTERNAL ANATOMY of the Libellula penis is illustrated 

 in Plate III. The most of this part of the study is based on 

 the penis of Plathcmis lydia because the writer happened to 

 have material of that species that could be sectioned. Fig. 16 

 shows the adult lydia penis in ventral and lateral views. Fig. 

 17 is a diagram, in shadows, of the penis of a last instar naiad, 

 as this organ lies in its temporary, larval sulcus at the anterior 

 end of the sternum of abdominal segment 3. In this stage the 

 apex (penis segment 3) of the penis is fully developed but the 

 shaft (segment 2) and the inflated base (segment 1) are still 

 only partially developed and are wholly unexpanded. By com- 

 paring fig. 17 with fig. 16, the difference between the two stages 

 can be seen. The vertical lines indicated by letters in fig. 17 

 locate the levels of the sections shown in figs. 18-25, each of 

 which bears a letter to correspond with its level on fig. 17. 

 The internal anatomy of the Libcllnla penis is simple. In its 

 adult condition it is merely a bag of cuticula lined with a layer 

 of hypodermis and containing, besides two tracheae, the re- 

 mains of the embryonic tissue which filled its cavity during its 

 development. Apparently this tissue breaks down at the emerg- 

 ence of the naiad, so that in the imago the penis interior is a 

 cavity continuous with the haemocoele of the body. Probably 

 erection of this organ is due to a sudden surge of blood from 

 the abdomen into this cavity. Fig. 25 is a cross-section through 

 the embryonic penis shown in fig. 17 at the level H, and show: 

 the connection of the embryonic tissue of the penis cavity and 

 the haemocoele of the abdomen. This is before the embryonic 

 tissue has disappeared. 



The penis has two external openings, one at the apex, be- 

 tween the medial lobes, which I have termed the distal meat us. 

 and one at the outer end of the penis, which I have termed the 



