THE SIZE OF INSECTS. 
169 
these as of other parasitic Hymenoptera are being found or reared 
and the family is probably an extremely important one. 
Scelio acte, Wlk., and Epyris orientalis, Cam., are recorded as well as 
Platygaster oryzce, Cam., bred from the maggots of Cecidomyia oryzce, 
W. M. A species of Scelio attacks the eggs of the Bombay Locust, 
Acridium succinctum , Linn. ; Hadronotus sp. and Telenomus sp., were 
reared from insect eggs and Telenomus sp. from the eggs of Scirpo- 
phaga auriflua , Zell., a Pyralid moth. Scelio (Homalotylus) terminalis, 
Say., is a parasite upon the larvae of Chilomenes sexmaculata, Fabr. 
THE SIZE OP INSECTS. 
We are told that on other planets, man might be very much larger 
than he is on earth on account of the less force of gravity due to the 
smaller bulk of the planet. That is, the Mammoth or some prehistoric 
reptile represents the maximum size attainable on earth simply because 
the bones requisite to support a larger animal and to bear the muscular 
strains set up in moving it could not, with the material of which bones 
are constructed, exist. Gravity and the tensile strength of the mate¬ 
rial used in making the skeletons of animals thus puts a limit at one 
extreme. On the other extreme is another limit in the size occupied 
by a sufficient aggregation of molecules to carry on the complex 
reactions of physical life, a limit which possibly admits of the existence 
of forms of life smaller than can be perceived by our present methods ; 
at any rate, there are organisms visible only under a magnification of 
thousands of diameters. 
Between these extremes lie our insects; the smallest are less than 
a millimetre in length : the largest moth has a wing span of twelve 
inches, the biggest beetle a length of over half this and the bulk of 
our insects are between three and one-tenth of an inch long and 
between five and a fifth of an inch across the expanded wings. 
Probably the essential feature in insect anatomy that has limited 
them in size is the chitinous integument; an insect has no bones, it has 
no separate internal skeleton round which the soft tissues can be 
grouped and which can give a central support to muscles and connec¬ 
tive tissue ; there is only an external integument, with processes 
internally, and the tissues take their attachment from this and are 
packed away inside it. There is further the delicate tracheal system, 
probably capable only of a certain amount of compression and thus 
limiting the amount of stress that can be set up by muscular action. 
Another point is that the chitinous integument is not, except in the 
adult stage, a permanent one ; it is shed and this puts a very definite 
limit probably upon the size to which it can be produced. 
