Objects for the Microscope. 139 



Prcebrachial vein connected with the cubital by a trans- 

 verse vein near the margin, and between the two is a faint 

 streak or spurious vein crossing a second transverse vein 

 nearer the base. 



The mediastinal areolet is coloured in this wing, and 

 appears like a narrow stigma between the sub-costal and 

 mediastinal veins. 



Areolets are enclosures formed by the branching and 

 crossing veins ; they are important in the wings of the 

 Syrphidse, and must be observed. 



All the Syrphida? have alula3, which are membranous scales 

 at the base of the wings, protecting and sometimes quite 

 covering the halteres. They are particularly beautiful in 

 Rlvnyia and Eristalis, and deserve to be mounted separately. 



In the wing of Helophilus the cubital vein curves sud- 

 denly inwards, forming a loop in the centre of the areolet. 



The feet of Syrphus are beautiful, and from the trans- 

 parency of the preparation we see the articulation of the 

 tarsal joints distinctly, the spine at each tarsus, and the 

 strong hooks and delicate pulvillus of the foot. 



Some of the Syrphidse have their abdomen nearly filled 

 with air, and partly diaphanous or transparent, when by 

 careful management the circulation of their blood may be 

 seen, and the pulsations of the dorsal vessel or heart may 

 be counted. Place the fly in a live box with just sufficient 

 pressure to keep it still, and between the segments the 

 fluid may be seen. The following extract from ' Walker's 

 British Diptera' (vol. i. page 285) will be interesting to the 

 student : 



" The dorsal vessel of this fly (S. pyrastri), instead of the 

 usual form which it had in the larvsej assumes the shape of 

 a flask, having its long end directed towards the thorax ; 

 the pulsation and transmission of the fluid in it is manifest. 

 This vessel extends in length from the junction of the trunk 

 with the abdomen to about the termination of the second 

 segment. The included fluid is propelled at intervals by 

 drops, first from the wide end towards the trunk, and then . 

 in the contrary direction. It is conjectured that the neck 

 of this vessel is composed of two or more approximated 



