41 8 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 antennae. 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 difiering 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 



