mero! 7 oe US, FETE USURPER-BEE 71 
abdomens, 16 young darbutellus queens, 2 small 
barbutellus males, and the body of the old darbutellus 
queen. The brood consisted of 38 Pszthyrus cocoons 
containing pupz, chiefly queens, and a cluster of 5 
hortorum cocoons containing younger pupe, all of 
which developed into males, besides a few larve and 
eggs. Probably therefore Ps. darbutellus is parasitic 
in the same deadly way as Ps. rupestrzs and vestats. 
There is a greater or less tendency in all the 
species of Pszthyrus to resemble their particular 
hosts in the pattern and colour of their coat. It can 
hardly be doubted that this is of some advantage 
to the Pszthyrus. 
The origin of Pszthyrus, more especially of its 
peculiar parasitical instincts, is an interesting question. 
If aspecimen of Pszthyrus be compared witha speci- 
men of Goméus it is seen that the resemblance is 
not merely superficial but extends to nearly all the 
important details of structure, so that it is impossible 
to avoid the conclusion that Pszthyrus has sprung 
from Loméus, and this at quite a recent period in the 
history of life. Moreover, the Aomdéz—and this is 
particularly interesting—show parasitical tendencies 
leading to the parasitism of Pszthyrus. We have 
seen (pages 55-58) how the Bomdbus queens may 
enter the nests of their own species and kill one 
another, and how, in the case of the twin species, B. 
terrestris and lucorum, terrestris has extended this 
habit so as to prey on Zucorum, killing the Zucorum 
queen and getting the /wcorum workers to rear her 
young in practically the same manner as the Psz¢hyrz 
