26 
retaining more nearly the characters and habits of their nonsocial 
ancestors. The development of the workers has not been confined, 
however, merely to the more highly specialized nervous system and 
instincts. In many of the ants and termites there are two, and some- 
times three or four, distinct kinds of workers, very different from 
each other and equipped with an equal diversity of instincts for 
undertaking special parts of the work of the social organization. 
One of the African termites has soldiers with immensely large heads 
and biting mandibles, whose sole function is that of defending the 
colony. When the wall of the nest is broken they sally out to en- 
gage the intruder. They are wholly devoted to this purpose, and 
lack even the instinct to return again, and soon perish from exposure 
to the drier, outside atmosphere. A second form of worker, also 
with large heads, but much smaller jaws, will not leave the nest: to 
fight, but appears to control the erection of new walls, though it does 
not itself carry earth, a work performed entirely by the third 
easte, which might be called the worker proper. These build the 
nests and bring in the dead wood, which, after a period of curing, 
is made into fungus gardens. The fourth caste is small and slender, 
and neither fights nor carries earth, but 1s occupied with the manage- 
ment of the eggs and, presumably, also with the feeding of the young 
larvee. 
We may be sure that this high degree of specialization of castes 
has come about during the period of social organization. How the 
queens are able to give birth to these distinct kinds of offspring 1s 
unexplained as yet, either by difference of nutrition or by any of the 
theories of hereditary transmission applied to the other groups of 
animals. 
Professor Weismann has appreciated the inadequacy of the nutri- 
tion theory, even with reference to the honeybee, and has attempted 
to explain the worker caste by means of his well-known theory of 
determinants.“ 
a“ This explanation [nutrition], however, even if correct as regards the degen- 
erated parts of the workers, does not sufficiently account for the other differ- 
ences between the two kinds of females. For the workers are not inferior to 
the queen bee in all respects. On the contrary, the worker’s sting is straighter. 
longer, and stronger, and is provided with more teeth than the queen’s. The 
wings, moreover, are longer, the tarsal segment of the hind limb is provided 
with the well-known brush, and the tibia has a depression known as_ the 
‘pocket’ for carrying the masses of pollen which the insect collects. These two 
characteristic parts are wanting in the queen. Important differences must also 
exist as regards the minute structure of the brain, for the instincts of the 
queen are very different from those of the workers. After fertilization has 
taken place the queen lays eggs, but she neither gathers honey from flowers, 
excretes wax, nor makes the honeycomb. It is therefore incredible that the 
queen and workers should be formed by the agency of similar determinants. 
