THE society's NOTE-BOOKS. 95 



it to say that the reasons I have for so thinking seems to me to 

 apply to the abdominal segments also. It will, of course, be seen 

 that if this is the case, the typical number, seventeen, is greatly 

 understated. It would seem, further, to come back to my starting 

 point, that from the marked character of the segmentation hitherto 

 recognised, such sub-segments, if they exist, must have been pro- 

 duced by duplicative subdivision of the former ; thus, roughly and 

 diagrammatically, for example (see Diagram, Fig. i, PL IV.), as 

 regards the thoracic segments. I hope I shall not be thought 

 overbold in this speculation, seeing that I am held in countenance 

 to some extent by no mean authority. I shall endeavour to direct 

 my attention further thereto. 



I should much like to see Rymer Jones's Outlines^ alluded to 

 by Mr. West. I gather that the external branchiae of Annelids are 

 herein regarded as the homologues of the tracheae of the Myria- 

 poda and Insecta, thus confirming a hint thrown out by Mr. Lowne 

 that these latter are true appendages developed inwardly. It will 

 be observed from Mr. West's drawing (PI. I., Fig. 4) that 

 the spiracles occur opposite the legs towards the dorsum imme- 

 diately beneath the lateral edges of the dorsal plates, just the very 

 position where they should occur as superior dorsal appendages. 



Arthur Hammond. 



Anatomy of Drone-Fly (PI. IV., Lower portion). — The ovi- 

 positor presents similar features to that of the Blow-fly, but the male 

 organs are different. The drawings are copies of some of my own 

 made some time ago. The eighth dorsal abdominal plate appears 

 by a curious process of torsion on the ventral aspect. The minute 

 chitinous spaces on the membranous part of the integument, 

 marked 5^., 6^., and 7^., are the fifth, sixth, and seventh dorsal 

 plates. This appears from the occurrence of spiracles between 

 them and the corresponding larger ventral plates, marked 5z^., 6?^, 

 and "jv. 



The bilateral symmetry usually observable in insect structure 

 appears here to be wholly wanting, as, indeed, it frequently is in 

 these parts. The plates seem to be twisted over, so that on the 

 dorsal aspect we see a little piece of the sixth ventral plate, a 

 larger piece of the seventh, and nearly the whole of the eighth ; 

 while on the ventral aspect the reverse takes place : we see nearly 

 the whole of the sixth, less of the seventh, and only a little piece 

 of the eighth. In the same way, the dorsal plates represented by 

 the eighth (for the fifth, sixth, and seventh are mere rudiments) 

 are presented on the ventral aspect. This may seem strange, but 

 an examination of the parts in their natural condition will show 

 that it is most difficult to determine what does follow the eighth 

 ventral plate from observation alone. I have therefore followed 



