Thorax in winged Insects. 155 



generalization of the anatomical structure of the. /^nntt/osa, as given in the 

 " Horce Entomologicce,"* was perhaps too much founded on an idea of 

 M. Latreille, and one of my principal objects now is to correct some mis- 

 takes which I have detected in what I formerly advanced, although with 

 doubt, upon this very difficult question. 



Every annulose animal, even including the Myriapoda, whose appa- 

 rent departure from the normal structure of Annulosa I shall elsewhere 

 explain, may be resolved into thirteen primary vertebral segments, which 

 are thus disposed, one for the head,f three for the thorax, and nine for the 

 abdomen. In certain cases, however, one or two of these abdominal 

 segments may be found intimately connected with the thorax, so that the 

 thorax may be said to consist of five segments. It is on this view of the 

 subject that a Squilla may be said to consist of thirteen primary segments, 

 that is allowing four secondary ones for the head, five very small primary 

 ones for the thorax, and seven for the abdomen. :J: On this view also a 

 Scorpion consists of a true and distinct head with twelve other primary 

 segments. Galeodes has the same normal structure, that is, a large head 



* See HoraeEat., Vol. I. p. 412, where I have hinted the possibility of what 

 Mr. Kirby calls the Alitrunk being' composed of four segments of the larva. 

 The test, however, which I then proposed, has since led me to a very different 

 conclusion. 



f The three or four secondary segments of the head can be reduced to one ; 

 or, which is the same thing, the head can in all Annulosa be shewn to be com- 

 posed of four segments or regions, when perfectly developed. For the present 

 I shall only refer to the following words of M. Audouin. " L'entothorax 

 " n'existe pas seulement dans le thorax ; on le retrouve dans la tete, et il de- 

 " vient un moyen assez certain pour demontrer que celle-ci est composee de 

 " plusieurs segmens." See Ann. des Sc. Nat., Vol. I. p. 125. 



J Perhaps, indeed, Crustacea may be said to differ from all other perfect 

 Annulosa, inasmuch as the first two segments of the abdomen in other Annu- 

 losa often in this class become thoracic, carry true feet, and leave only seven 

 segments for the true abdomen. As to the head, the truth is, that when fully 

 developed, it is composed of a tergum and a. pectus (here called a. fades and a 

 subfaciesj, like one of the three primary segments of the thorax. In the head 

 of a Squilla we may observe four series in the fades, which clearly answer to 

 i\ie prxwutum, scutum, scutellum, a.nd vnstscutellum o{ a. mesothorax. 



