i8o THE INTEGUMENTAL SKELETON OF THE IMAGO. 



view that the diaphragma represents the inflected post- 

 scutelUim, either in the prothorax or the mesothorax, but 

 think it is indubitable that the prodorsal arch and the 

 paratremes represent the collar of the Hymenoptera. 



With regard to the morphological significance of the cervical 

 sclerites, amongst which I have included the sella, they must 

 either be regarded as a portion of the complex prothorax, or as 

 the remains of one or more segments which are no longer 

 distinct in either the embryo or the nymph. I prefer to regard 

 them as prothoracic. Complex prothoracic sterna are fre- 

 quently seen even in the Orthoptera, for example, in the 

 greatly elongated prothorax of Mantis ; and, as I have already 

 observed, the structure of the meso- and metathorax is no 

 guide to that of the prothorax. 



The prothorax appears to mc to exhibit strong indications in 

 favour of the view held by Patten and others that the thoracic 

 segments have resulted from the fusion of two or more primitive 

 metameres. But any attempt to determine their limits, or even 

 their number, in the absence of direct developmental evidence, 

 could be nothing but guesswork, although it is evident that 

 many metameres have disappeared in the process of evolu- 

 tion. 



The Nomenclature of the Spiracles. — Whether the anterior 

 spiracle should be regarded as prothoracic or mcsothoracic, or 

 the posterior as metathoracic or abdominal, has given rise 

 to much discussion, which I regard as futile, although the 

 views in which it originated are of some interest. Oken's 

 idea of the origin of wings from respiratory organs was 

 adopted by Latreille and De Blainville, and Blanchard ap- 

 pears to have considered them as everted tracheal sacs, the 

 thoracic attachments of which are homologous with the 

 spiracles, and this led him to assert that ' there is never any 

 spiracle on either the meso- or metathorax of a winged insect,' 

 an opinion which has been frequently repeated. Palmen 

 showed that the tracheal gills of Ephemera arise independently 

 of the spiracles, and are in no way mere modifications of 

 them, and Blanchard's statements rest solely on the fact that 



