25 
all parts of the nests, so that the application of a consistent regimen 
of feeding would become, humanly speaking, impossible. 
In some of the relatives of the kelep native in Texas, Professor 
Wheeler has found that there is no clear distinction between the 
fertile females and the workers, a condition which he ascribed to the 
desultory feeding habits of the insects.¢ The deficiency may be con- 
nected, however, with the more backward social organization of the 
Texan species. The keleps, with the same predaceous habits, seem 
always to be able to produce the two well-defined types; at least no 
intermediate forms have been observed. 
The question has not been put to an experimental test as yet, but 
the suggestion has arisen in connection with the kelep that the de- 
velopment of a larva into a worker may be brought about in the early 
stages by withholding food, it having been noticed that the larvee 
grow very slowly at first, but after they reach a certain size they often 
complete their development with great rapidity. A superabundance 
of food or a special solicitude for the younger larve might induce 
the development of queens without the necessity of supposing that 
the insects proceed by any deliberate intention. 
But even among the keleps the worker caste is hardly to be 
explained merely by inadequate nutrition, for the reason that it 
possesses positive as well as negative characters and instincts which 
the queens do not have, and which they probably never had in the 
evolutionary history of the species. As previously stated, it is well 
known that among the bees and ants the nervous system, and 
especially the part which corresponds to the brain of the higher 
animals, is much more highly developed in the workers than in the 
sexually perfect insects, and this is accompanied by the accentuation 
in the workers of the social instincts by which the colony is main- 
tained. 
HIGHLY SPECIALIZED WORKER CASTES. 
The more recent evolutionary changes among social insects have 
been largely in the direction of the workers, the males and females 
a*“* Now, while we can, perhaps, understand how these more specialized ants 
may manage to control the quantity and quality of liquid food regurgitated 
from their own crops and salivary glands, it is not so easy to understand how 
ants can exercise such control when they adopt a capricious method of feeding 
like that of the Ponerinz. Such a method can hardly produce clear-cut results, 
i. e., either workers or fertile females. And a comparative study of the better- 
known species of Ponerinze shows that in certain species, at least, there is no 
such sharp distinction between the sterile and fertile female as we find in the 
more specialized ants. Not only is the female sex in a state of morphological 
and physiological instability—i. e., di- or even tri-morphic—but the male sex 
also is sometimes dimorphic, at least in the same genus, if not in the same 
species.”—Wheeler, W. M., 1901, Biological Bulletin, 2: 28. 
28929—No. 10—05 m 4 
