418 TRANSFORMATIONS OF INSECTS. 
animal, but by the force of expansion of the growing body, the 
development of which being greatest along the line of the back, 
exerts in consequence a greater degree of force against the middle 
of the dorsal than the corresponding part of the ventral surface. 
The head and tail of the embryo act as a fulcrum against the 
ventral surface only at the ends of the shell, and thus bend it 
into the kidney-shaped form it assumes while the dorsal surface 
of the embryo is gradually pressed through the opening. From 
the comparative rapidity of its enlargement immediately after the 
shell is fissured it seems as if the stimulus given to it by exposure 
to a new medium—atmospheric air—were the great means of 
exciting its evolution. 
The embryo is now formed of eight distinct segments (Fig. 3), 
including the head, the ninth or anal ring being still indistinct. 
The head is more defined in its outline, and exhibits at its sides 
a faint trace of the future antenne. The four thoracic segments 
also exhibit on their ventral surface little nipple-shaped extensions, 
three of which on each side are the rudiments of future legs. Mr. 
Newport was unable to detect any separate internal organs, the 
whole embryo being made up of a mass of cells, in the midst of 
which there appeared to be some traces of the commencement 
of the alimentary canal. On the third day the embryo had 
increased considerably in size, but was still perfectly motionless. 
The rudiments of the legs were more developed, and, indeed, the 
creature is then apodal, or legless, for several days after bursting 
its shell, the future limbs being in a very rudimentary state. 
Some faint traces of a single eye or ocellus on each side of 
the head were discerned on the fourth day, and there were traces 
of the formation of the internal organs. Internally the body was 
still formed of cells, aggregated together, but differing more in 
size than at any previous period, as if they were becoming fused 
into separate tissues, and in the midst of them, and closely sur- 
rounded on all sides, was the newly-formed alimentary canal. 
Around the sides of the body muscular structure was also in course 
of development, but as yet was exceedingly indistinct. The legs 
had become larger and more obtuse, and the embryo was still 
motionless and incompetent to take on spontaneous movements. 
On the third day the posterior part of the body is less distinctly 
