26 MR. A. HAMMOND OK THE 



their insertion in another*, and that where two segments are 

 concerned there is sure to be more or less repetition of the mus- 

 cles presented to view. 



Let us glance for one moment at the muscular structure of 

 jEslma grandis. This insect is remarkable for its power of flight, 

 and yet, contrary to the general rule, the longitudinal muscles are 

 almost obsolete, the deficiency being made up by the number and 

 high organization of the vertical ones. The alary segments are not 

 very clearly separated externally, but internally an inspection of 

 these vertical muscles shows clearly that the united cavity they 

 occupy is formed of two segments. After removing the two 

 principal masses which towards the mesial line are attached to 

 the bases of the wings, and which obstruct the view of those 

 behind, we find a number of others which have their insertions 

 formed in a peculiar and very beautiful manner by a round plate, 

 or " cupule " as Chabrier calls it, to the concave surface of which 

 the muscles are attached, while from the other proceeds a tendon 

 to the point requiring motion. These muscles, with the excep- 

 tion of the last, are repetitions in two sets, 123 4, 1234 (see 

 PL II. fig. 14), showing the existence of two segments. 



But there is no such repetition in the vertical muscles of the 



* If there be any doubt felt as to the correctness of such an assumption, let 

 us look a little further into the matter. Passing by my own observations on the 

 point, though the statement is founded mainly upon them, I may refer to 

 the figures of Lyonet, in his Anatomy of the Larva of Cossus ligniperda, and 

 to Sir John Lubbock, " On the Larva oiPygcera bucephala," Linn. Trans, vol. xxii. 

 p. 173. Of the following corresponding lateral muscles in the two insects, 

 viz. 



a Lyonet = 37 ? and 38 Lubbock, 



|3 



»> 



=49 and 50 



r 



>) 



= 46, 47, and 48 



8 



>> 



= 51 



K? 



» 



= 33 and 34 



e? 



>> 



= 35 ? and 36 



m 



i> 



= 40 



n 



»> 



= 43 



only the four marked thus (?) appear to offer a shade of doubt in this respect ; 

 and these cases are indeed, as I may say, doubtful ones. The question is not ex- 

 actly whether they actually cross the border-line between the segments, but rather 

 whether they are attached by one extremity thereto, and that, in the case of 6 = 35, 

 only in a partial sense, the anterior fasciculi only being in question. 



