A. D. Imms 
119 
the thoracic buds are relatively very large in size, and are superficial in 
position, lying just beneath the integument. At first they each have 
the structure of simple buds (Fig. 19) of thickened hypodermis, 
enclosing a small amount of “mesenchymatous” tissue, but, by the time 
the larva has become fully grown, they are seen to exhibit a high degree 
of specialisation. The dorsal prothoracic buds have become the com¬ 
pletely formed respiratory trumpets; those of the mesothorax are 
highly complex organs (Fig. 25), and are much folded and plicated. 
They already exhibit a wing-like character, the hypodermal cells being 
greatly drawn out at right angles to the surface of the bud, assuming a 
pillar-like form, and the upper and lower hypodermal layers meet and 
fuse with one another. In places they are excavated into hollow tube¬ 
like spaces which are forerunners of certain of the future nervures ; the 
dorsal metathoracic buds remain in a more generalised condition, being 
the smallest and least advanced of the series. The leg-buds are at this 
period long tube-like organs which are bent upon themselves. 
III. The imagined buds of the abdomen comprise a dorsal and 
ventral pair situated on either side, near the hinder extremity of the 
body. The dorsal pair of buds form the pupal tail fins; they are placed 
one on either side of the eighth abdominal segment, and lie within the 
cavity of the supporting skeleton of the larval spiracles (Figs. 7 and 8). 
They exhibit very much the same structure as the buds of the wings, 
the hypodermal cells being enormously drawn out at right angles to the 
surface of the organ and the protoplasm reduced to narrow strands in 
which are distributed extremely small nuclei. They are greatly folded, 
on account of being confined within a limited space, and investing the 
free surfaces of the folds is a well developed cuticle. They are situated 
within the lateral plate (sc.) of the spiracular skeleton, and project freely 
backwards reaching to the transverse chitinous band ( t.b .), and thus lying 
beneath the spiracular lobe. They appear to differ from the other buds 
in being directly formed by modification of the hypodermis, without the 
latter being previously invaginated to form a pocket, and from the 
bottom of which the buds arise usually as finger-like evaginations. On 
this account, the buds of the pupal fins are not enclosed within an outer 
wall or peripodial membrane. 
The second pair of buds (Fig. 28) are ventral in their position, and 
placed close to the points of origin of the outer vertical muscles 
(o.mus. in Fig. 5) of the spiracular apparatus. These buds like the 
rest lie immediately beneath the hypodermis, and maintain a free 
communication outwards by means of the mouth of the original 
8—2 
