1909.] NATURAL SCIENCES OF PHILADELPHIA. 41' 



that the salivary glands are modified tracheae, to explain the fact that 

 the prothorax has no spiracles. Comstock claims that the prothoracic 

 spiracles are drawn along with the migrating maxillae and, becoming- 

 united, form the opening of the salivary glands, into which their corre- 

 sponding tracheae have changed. He regards the lateral cervicals as 

 the episternum and epimeron of the labial segment, and the internal 

 process between these he explains as the endopleural apodeme of this 

 "segment." Voss, '04, arrived at much the same conclusion from his 

 study of the musculature, and Riley likewise considers that the cervical 

 sclerites belong to the second maxillary segment, from his embryological 

 investigations. 



The third theory is that of Newport, '39, who proposes that the 

 cervical sclerites are detached portions of the prothorax, and repre- 

 sent the paraptera (laterale?) of the meso- and meta- thorax. Borner, 

 '03, likewise considers that the cervicals are prothoracic plates which 

 have become detached from the sternal region of that segment. 



In an earlier paper (Crampton, '08) it was suggested that the cervi- 

 cals possibly correspond to the "intersegmentalia" found between the 

 pro- and meso-thorax, and that the internal hollow process between the 

 lateral cervicals might represent the remains of the trunk of a pro- 

 thoracic trachea. It is quite comprehensible that a strongly chitinized 

 tracheal stem, such for example as that of a Perlid, could serve as a 

 muscle support, and, furthermore, it is possible for muscles to become 

 attached to the tracheae without interfering with their respiratory 

 function, as is shown in certain Arachnoidea. In the case of the pro- 

 thoracic tracheae, it was proposed that their trunks, being in a favorable 

 position to serve as a support for the head muscles, were preserved by 

 a change of function, while the remaining portion of the tracheae would 

 be subjected to the same influences which caused the disappearance of 

 the tracheae in the buccal somites. 



This theory would seem no more improbable than Comstock's, '02, 

 view that the apodemes of the pro-, meso- and meta-thorax are tra- 

 cheal vestiges, and is by no means so startling as Carriere's, '98, theory 

 that the salivary glands are modified tracheae. Indeed, the views of 

 Palmen, '77, Hatschek, '77, Wheeler, '89, and Carriere, '98, who 

 claim that the tentorium (which likewise serves as a muscle support) 

 is composed of modified tracheae, render the theory that the cervical 

 apodeme is a modified trachea all the more probable; and Palmen's,. 

 '77, statement that there are traces of a tracheal invagination in the 

 neck region of the embryo likewise lends weight to the above-men- 

 tioned theory. However, upon looking into the subject more carefully. 



