2G6 



PTILOTA: IMAGO EXTERNAL ANATOMY. 



Audouin, amounts to thirty-six ; but if the simple pieces, as 

 the sternum, &c., be supposed to be divided by the medial 



Vi K s. 121, Proternum-122, Mesost 



line, the number will be fifty-two ; and Mr. MacLeay, by 

 supposing that each of the three sterna consists, like the 

 terga, of four transverse pieces similarly divided by the me- 

 dial line, considers the whole number of pieces in the thorax 

 to mount up to seventy-two. Authors, however, who have 

 looked at the composition of the thorax, without having any 

 theoretical views to maintain, have found the really distinct 

 number of its parts much fewer in number than either of 

 the last-named authors: thus Chahrier and Burmeister 

 reckon only eighteen, Kirby and Spence twenty, and Strauss- 

 Diirckheiin twenty-two. We will now confine our attention 

 successively to the primary segments of the thorax, and 

 show the chief modifications which they exhibit, and then 

 describe the organs of locomotion. 



