PETS. 77 
ants, but while some associate with several species, 
many are confined to a few or even to one. 
V. Hagens is of opinion! that in some of these 
beetles which frequent the nests of two or more species 
of ant, varieties have been produced. Thus he has 
observed that the specimens of Thiasophila angulata 
in nests of Formica congerens are darker than those 
found with F. exsecta. Heterius sesquicornis found 
with Lasius niger and Tapinoma erraticum are 
smaller than those which occur in the nests of larger 
ants; and the form of Dinarda dentata, which is met 
with in nests of F. sanguinea, has ratber wider wing- 
cases than the normal type. 
I would by no means intend to imply that the 
relations between ants and the other insects which 
live with them are exhausted by the above suggestions. 
On the contrary, various other reasons may be imagined 
which may render the presence of these insects useful 
or agreeable to the ants. For instance, they may emit 
an odour which is pleasant to the ants. Again, Mr. 
‘Francis Galton has, I think, rendered it very probable 
that some of our domestic animals were kept as pets 
before they were made of any use. Unlikely as this 
may appear in some cases, for instance in the pig, we 
know as a fact that pigs are often kept by savages as 
pets. I would not put it forward as a suggestion 
which can be supported by any solid reasoning, but it 
1 Berlin, Ent. Zeit. 1865, p. 108. 
