204 



HARDWICKE'S SCIEN CE- GOSSIP. 



tarsi, being easily distinguishable : they appear to 

 be ultimately released by the bursting of the cap- 

 sules, and may be seen on the ventral surface of 

 the pupa, packed closely side by side, and slightly 

 attached to the surface by, a sort of gummy ex- 

 udation. 



Fig. 130. 



therefore, to these last-named organs, I think there 

 is little doubt that the above statement is correct ; 

 the only question in my mind is with regard to the 

 development of the spiracles from the superior 

 prothoracic discs, inasmuch as I am not quite cer- 

 tain whether these are to be regarded as the superior 



Fig. 131. 



Fig. 129. The mentum and muscles attached from beneath : 

 men, the mentum ; n, levator ; m', depressor muscles of the 

 mentum ; m", muscles connected with sd, the salivary duct; 

 gg, ganglia; as, the oesophagus. All slightly magnified. 



Fig. 130. Portions of muscular fibre with myolemma, assum- 

 ing a cellular form from pupa, X 50. 



Fig. 131. Poition of trachea with outer and inner coats, the 

 latter being doubled owing to the formation of a new 

 ringed coat around the old one, x 210. 



The three superior pairs of thoracic discs are 

 found close to the former, but a little more removed 

 towards the dorsal surface. The organs within 

 them are not so easily distinguishable as those just 

 mentioned, but they are, I believe, as follows. The 

 superior prothoracic discs are concerned in the 

 formation of the anterior thoracic spiracles, the 

 corresponding discs of the mesothorax in that of 

 the wings, and those of the metathorax contain the 

 future halteres. I have not been able as yet to 

 observe the growth of these organs within the discs, 

 but my reasons for thinking so are as follows. It 

 would appear that the organs of the imago which 

 are subject to this mode of development are the 

 appendages, inferior and superior, proper to the 

 segment in which it occurs ; and the question there- 

 fore seems to resolve itself into another ; viz., which 

 are the appendages proper to the segments in 

 question. Now it is generally recognized, I believe, 

 that the three pairs of legs form the three inferior 

 appendages of the thoracic segments, and that the 

 wings and halteres represent the superior ones of 

 the meso- and metathorax respectively ; with regard, 



Fig. 132. 



Fig. 133. 



F"ig. 132. One of the abdominal ganglia of the ventral cord, 

 showing the outer and inner coats, the ramifications of the 

 trachea? between the two, and the two pairs of nerves 

 arising from it at aa and a'a' x 12". 



Fig. 133. The cerebrum and nerves attached from above: cc, 

 the lobes of the cerebrum upon which trachere are seen to 

 ramify ; aa, the antennal nerves of the larva j a'a', those of 

 the imago. Both these are seen to form arches, one to the 

 frontal sympathetic ganglion at fg, and the other to the 

 fork above it at /; // are branches to the labrum ; 00, the 

 optic nerves; sn, the single sympathetic nerve (nervus 

 recurrens) ; g, the ganglion beneath the cerebrum connected 

 by fine nervous filaments with the pair of sympathetic 

 nerves sn' sn', which arise from the posterior portion of 

 the cerebrum, slightly magnified. 



appendages of the prothorax. Now Mr. Lowne, 

 though he does not speak positively on the subject, 

 evidently regards the spiracles and their trachea; as 

 lateral appendages, like the wings and legs. This, 

 therefore, tends to support my view, which is still 

 further strengthened by an examination of the pupa, 

 on which I find two club-shaped organs,* springing 

 from the dorsal region of the prothorax, and which, 

 from their form and position, I find it difficult to 

 regard in any other light than as the appendages in 

 question. Now, the main trachea?, in the pupa pass 

 up the centre of these organs, emerging from the 

 imperfectly formed spiracles of the ily beneath. 1 

 therefore regard them as the cases or sacs within 

 which the spiracles are developed, in the same way 

 as Ihe wings, legs, &c, are formed within the cases 

 proper to them; and as these result from the per- 



* In the- pupa of the gnat these organs are very conspicuous. 



