On the Pijgiclia and Cerci of Insects. By Henry Davis. 253 



will be a safe, because an under, statement to say, that without any- 

 special search, fifty insects of different species are now proved to 

 possess pygidia. The organ is here spoken of in the plural, as 

 with the single exception furnished by Piilex, all the insects 

 examined have it in pairs more or less sej)arated ; even in the Flea 

 it is distinctly double and bilateral, and I submit it should no 

 longer receive the singular appellation except when divided. 



It would doubtless be satisfactory to give a full Hst of all the 

 insects on which I have found pygidia, but it happens that by far 

 the greater number are exotic, taken, some at the Cape of Grood 

 Hope, some in Mauritius, and other places abroad ; the correct 

 naming is a difficult task ; even Mr. Frederick Smith of the British 

 Museum shrank from it, and I am constrained to speak of the 

 foreign species in general terms, but will give particular examples 

 in common English insects. 



The pygidia of the Lace- wing may be taken first, as introductory 

 to a series gradually increasing in size ; they are found as nearly 

 circular, flat, or slightly convex plates, one on each side of the last 

 (posterior) joint of the abdomen ; they are dorsal, and only require 

 to be pushed (so to speak) closer together to be exact copies of the 

 pygidia of the Flea. It has a similar collection of the same shaped 

 areolae and the same characteristic fine long central hair. Next to 

 this, as having pygidia of the nearest resemblance to that of the 

 Lace- wing, comes the common small Grasshopper {Gryllus) ; in this 

 the organs project slightly, conical in figure and somewhat flattened 

 at the sides, but otherwise they are exactly similar to the only 

 pygidia hitherto known. In the large Grrasshopper {Acrida viri- 

 dissima) the parts are much longer and not easily overlooked, 

 while in the Cricket {Acheta domestica) we find these same organs 

 extended to an immense length — sometimes three-quarters of an 

 inch — but still bearing the peculiar structure of rayed and haired 

 areolae. The Mole Cricket {Gryllotalpa vulgaris) also has large and 

 ■beautifully marked pygidia. 



In the Cock-roach {Blaita orientalis) may be found correspond- 

 ing large appendages, which are called cerci by Burmeister ; except 

 in position, there is little at a glance to identify them with the 

 parts we have seen. They are nearly bare on the superior surface, 

 and t]ie under side, often turned upwards and outwards, only is 

 furnished with any long hairs; nor are these set in broad, deep 

 sockets like those described, but are attached to small, clear, unrayed 

 spaces, flush with the chitinous integument. To found a belief that 

 these cerci are really pygidia, it requires considerable acquaintance 

 with the latter's various modifications, and, above all. a knowledge 

 of the very peculiar properties of the long hairs to be mentioned 

 presently. 



Of foreign insects having pygidia, I purpose saying little, 



