52 PROCEEDINGS OF THE ACADEMY OF 



These wings are pervaded b} r numerous minute divisions of the 

 trachea, which, by the violent motions of the wings, are sup- 

 plied with a superabundance of air, the necessary consequence of 

 redoubled vigor. The continual pressure of fresh accessions of 

 air upon what already exists in the above vessels, exerts an ex- 

 pansive influence upon the wings, which ultimately assume con- 

 figuration. Such being a faithful statement of facts as we find 

 them, there can be no hesitancy in assuming that a change of con- 

 ditions as above indicated, in the animal's violent struggles for 

 existence, would so react upon its hitherto quiescent spiracles as 

 to conduce to their functional activity. Like the adult Lepidosiren, 

 there may 3'et be discovered some unknown Paraponyx which 

 possesses these gills only during its early larval history. The 

 presence of gills and spiracles in the known specimen, argues in 

 favor of its derivation from a type that possessed gills alone. If 

 these spiracles are quiescent, and only become active in a measure 

 during the period of pupation, as has been presumed, the passage 

 into forms that possess this gill-breathing power during their 

 early larval period, and thence into others that have completely 

 renounced it, is exceedingly gradual. Some of these Eydrocam- 

 pidse, it is affirmed by Duncan in his " Transformations of In- 

 sects," have branchiae or gills, and exist surrounded and bathed 

 by water. This fact conducts to the inference that they are 

 wholly gill-breathers. From a Paraponyx possessed of both gills 

 and spiracles to the Phryganea, is but a moderate transition. 

 However, it is not presumed that said Paraponyx has been imme- 

 diately derived from a Phryganea, neither is it predicated that 

 the complete gill-bearing form has been the proximate descendant 

 of a Phryganea. But so closely do the larvae of Paraponyx in 

 form and habits resemble existing Caddice worms, that the con- 

 clusion based upon their near relationship, seems irresistible. 

 Ma3 T not the branchia-bearing form of Paraponyx have been the 

 immediate descendant of some pre-existent form of similar habits, 

 but of closer resemblance to Phryganea, in details of form and 

 structure, in a state of maturit} 7 ? Acting upon this consideration, 

 I have presumed their derivation from a form at present unknown, 

 which I have previously designated the ideal type. 



Having somewhat lengthily detailed the truths which have led 

 to the views expressed in this paper, it becomes me to put them 

 to a proper test. With a view to give tone and character thereto, 



