PARTS OF INSECTS. 99 



already been fully discussed. As I have not, however, seen them 

 before enunciated in the form they have presented themselves to 

 me, I will, with the kind permission of my friends, risk their 

 advancement in these pages. The repetition of similar parts in 

 successive rings or segments, distinctive of the Arfiadata, has 

 always appeared to me to form one of the most interesting points 

 of inquiry in connection with the study of insects. 



How far is it possible to trace this repetition ? The recogni- 

 tion of the fact by Savigny and others that the organs of mandu- 

 cation are the proper articulated members of distinct segments, 

 the homologues of the organs of locomotion on the succeeding 

 ones, suggest at least the possibility that other relations of a like 

 nature may be observed. Mr. B. T. Lowne, in his " Anatomy of 

 the Blow-Fly," p. 3, says : — " Each segment in the lowest articulata 

 is normally furnished with two pairs of lateral appendages or rudi- 

 mentary limbs, one pair placed above the other, the superior being 

 dorsal and the inferior ventral ; at least, such is their arrangement 

 in annelides. Both pairs are much modified in the higher forms, 

 and are often entirely suppressed. The segments themselves may 

 be said to consist typically of four plates : a ventral, a dorsal, and 

 a lateral plate on each slide; the superior appendages being placed 

 between the lateral and dorsal, and the inferior between the lateral 

 and ventral plates. In insects the wings, when they exist, repre- 

 sent the dorsal appendages, being placed between the superior 

 and lateral plates." From this we may gather that the wings of 

 insects are the superior pair of the two with which each segment 

 is normally furnished. Now, I have not as yet met with any sug- 

 gestion that the organs which are thus admitted to be normal 

 parts of the skeleton may be traced in other than the wing-bearing 

 segments, and yet what are the alternatives? Either that the 

 wings are not normal parts of the structure, but something super- 

 added ; or that, being so, they are entirely suppressed in all the 

 other segments. Either hypothesis appears more or less satisfac- 

 tory, and the following considerations, derived originally from the 

 study of the common cockroach, appear to me to offer at least a 

 partial solution of the difficulty. But in order to show how the 

 relations of the dorsal plates must necessarily be viewed when 

 uncomplicated by the presence of wings, and at the same time to 



