1869.] 275 
forcing her way through tho earthen wall just after it is closed in. There she eats 
the egg of stercorarius, a mass as large as herself, greater, I suspect, if reckoned 
by weight. My observations do not show how long this takes her, but I should, 
judging from the different stages at which I have seen the operation, consider a 
week as about the time employed. When this is completed, she succeeds in quitting 
the tunnel. The eggs of A. yiorcus are laid, each by itself in a little spherical 
cavity, as carefully formed as that of stercorarius, though not lined with earth, but 
similarly much larger than the egg itself, which is almost a sphere of a little under 
^ inch ^in diameter. These little cavities are irregularly disposed in the pabu- 
lum surrounding the cavity made by stercorarius, the space of which is, finally, 
almost entirely used up in affording the spaces around 'porcus' eggs, I have 
counted as many as ten porcus' eggs so disposed, and believe there were frequently 
more, in instances in which I did not count them. In the mean time, the egg of 
stercorarius becomes flaccid and finally disappears ; and I have several times seen 
A. porcus* nose applied to it, as if discussing its contents. 
As to the extent to which A. porciis destroys the eggs of stercorarius, I have a 
note, dated Sept. 21st, 1868, that I brought home the contents of 29 tunnels, on ex- 
amining which, 15 appeared undisturbed, 6 contained porcus at work, and 8 had 
been visited and quitted by porc^is. In these, the only cavities present were those 
around porcus' eggs. No trace of stercorarius' eggs remained, and only the dis- 
turbed clay represented its surrounding cavity, J.. ^orcMs having completed her work 
and disappeared. 
On another occasion (Oct. 6th), I took 13 A, porcus in the tunnels of 0. ster- 
corarius, under one patch of cow dropping. In this instance, only a fourth of 
stercorarius eggs were undisturbed by A. porcus. On two occasions, I have found 
three A, porcus in one egg cavity, and several times two. I did not ascertain 
whether these were $ and ? , but suppose them to be females accidentally met on the 
same errand. 
I have never taken A. porcus elsewhere than in the egg cavity of Q. stercorarius' 
nest, except on one occasion, when, for the purpose of making this comparison, I 
instituted a careful search for it in the loose dung lying on the surface. In about 
an hour I found four. I then devoted an equal time to a search in their favourite 
habitat beside stercorarius' egg, and found twelve. Though several common 
Aphodii and other beetles swarmed in the droppings beneath which stercorarius was 
at work, I never found any other beetle in his burrows, except an occasional elytron, 
as though only the remains, after some predaceous beetle had devoured it, had been 
accidentally brought down with the stores of pabulum. I once found the remains 
of a beetle squeezed flat against the end of a burrow, obviously by the tight-packing 
process of G. stercorarius. This, on examination, proved to have been an A. porcus, 
which had probably gone down a little too soon. In undisturbed tunnels, no tracea 
of such eggs as those of porcus could be found, though a small larva (Aphodian ?) 
occasionally occurred somewhere in the length of tho burrow, tho egg having 
probably been accidentally brought down. These observations prove that A. porcus 
destroys the egg of G. stercorarius, replacing it by her own. Some doubt may 
exist as to her eating it, aa it is possible that it is injured by her tibite, &c., and that 
its contents soak into the surrounding material. Still, were this so, the egg would 
surely sometimes escape : its disappearance would not exist pari passfi with porcus' 
