244 WALKER ON 



In describing what I have seen, I have abstained from using 

 the word vessel, except where the margins were distinctly to 

 be defined, although I am inclined, from what I have seen, to 

 be of opinion, that a much greater portion of the circulation 

 than we can clearly define is carried on within given vessels, 

 as the blood may frequently be seen flowing in curved and other 

 lines, and confined within very narrow limits, but so deeply 

 seated amidst the muscles and intestines as totally to prevent 

 the boundaries of the current from being clearly observed. 

 This is strikingly the case in the side-view of this insect, 

 where currents are seen winding about in many diflferent 

 directions, but, from the intervening muscles and intestines 

 their boundaries are not visible ; nor can it be expected under 

 such circumstances, when we consider that the blood is a 

 perfectly colourless and transparent fluid, visible only from 

 its containing a number of particles of a somewhat flattened 

 oat- shape ; and that the great dorsal vessel itself is only to 

 be seen distinctly with a very high power, and even then can 

 only be defined with certainty whilst it is in motion. 



I cannot omit observing a singular coincidence between the 

 flattened oat-shaped particles of the blood in the insect, and of 

 the circular double concave plates in the human blood, which 

 is, that the particles of the former, like those of the latter, 

 assume a globular form immediately on coming in contact 

 with water. 



Art. XXVI. — Observations on the British Species of 

 Sejjsidcs. By Francis Walker, Esq. F.L. S. 



Micropeza was the generic name given by Meigen to 

 Musca corrigiolata, of Linnaeus ; or, Calobata corrigiolata , 

 of Fabricius, who has placed in the latter genus some Dip- 

 terous insects, having not the slightest aflSnity to each other ; 

 one species being a Sepsis; another, a Tachydromia ; a thii'd, 

 a Borborus ; their only mutual resemblance consisting in the 

 rapidity of their movements. Latreille, in his Genera Crust, 

 et Insect., has placed Musca cynipsea, of Linnaeus, and 

 Tephritis macula, of Fabricius (both belonging to Sepsis, 



