BY T. G. SLOANE. 575 



JEnigma. The matter becomes far more intricate when we 

 come to G. loiigipenne. All the other species of Gigademn 

 have the mentum without the long points to the lobes that are 

 found in G. lotigipenne, and have the inner lobe of the maxil- 

 lae with a strong triangular median prominence in the middle 

 of the inner side. Only in G. longipenne do these parts re- 

 semble the form found in Helluo; but G. longipenne is cer- 

 tainly a Gigadema, and not a Helluo, nor, as far as I can see, 

 is it a representative of the primitive type of Gigadema. I 

 believe the ancient type of Gigadema is represented rather by 

 G. sulcatum. In my conception of the phylogeny of the species 

 of Gigadema, G. longipenne is far removed from G. sulcatum, 

 and more allied to (t. nocte. It probably branched at a remote 

 period from the stem of which G. nocte is a present-day repre- 

 sentative. [The corneous, rudimentary paraglossae of G. longi- 

 penne, resembling those of G. hostocki of the G. nocte-grow^ 

 (together with other characters), have helped to influence me in 

 coming to this conclusion.]. If this view be correct, the maxil- 

 lae of G. longipenne have converged towards those of Helluo 

 by an independent reversionary line in the direction of the 

 ancient type from which both Gigadema and Helluo are de- 

 rived, and leading away from its congeners. In this case, an 

 inherited tendency towards ordinary maxillae may have help- 

 ed, as an influence of reversion ; but, it is also a case of con- 

 vergence, or, it may be said, of reversionary convergence. 

 With the simplification of the maxillary lobe, the long, point- 

 ed lobes may have arisen by correlation, but, still, also as a 

 case of reversionary convergence. 



The long, curved, sharp, horn-like points of the lobes of the 

 mentum in G . longipenne, which are formed by the epilobes, 

 may be an example of the cause which often seems to result in 

 many different parts of the body throughout the animal king- 

 dom, such as ornaments, weapons, or even structures which do 

 not seem of vital importance, becoming so exaggerated in their 

 development, that their presence would appear to be a detri 

 ment, rather than a benefit, to their possessors. Such cases of 



