140 On the larva of Pelophila. 
RELATIONSHIP OF PELOPHILA TO OTHER CARABIDS. 
The combination in the grub of Pelophila of structures 
characteristic of the Notiophilina, Nebrina and Elaphrina 
suggests that we have to do with an archaic type near to 
the common ancestors of these tribes, a view supported 
by the restricted northern range of Pelophila and the 
small number of its species. Also the similarity in 
several points between the grub of Pelophila and those 
of harpaline beetles gives evidence that it must be re- 
garded as a generalised member of the Carabidz since it 
shows affinities with such dissimilar types. There can be 
little doubt that the possession of long abdominal cerci is 
an archaic character, when we consider that such append- 
ages are found in primitive insects such as the Thysanura, 
Ephemerids and Perlids. The fact that in the young 
larva of Pelophila the cerci are comparatively short, and 
fixed, might indeed be thought inconsistent with such a 
view. But it is possible to regard the persistence of this 
condition of the cerci in the great majority of carabidous 
larvee as an instance of arrested development. The long 
legs of the larve of Loricera, Notiophilus, Nebria and 
Leistus, the head constricted behind into a narrow neck, 
and (in Lezstus and Notiophilus) drawn out in front into 
long spinose processes, appear on the other hand to be 
specialised characters, adapted to ready and rapid motion. 
From such a larva as that of Pelophila, then, can be 
derived, on the one hand, those of the Nebriina and 
Notiophilina, in which the head and legs have become 
highly modified while the primitive cerci have been 
retained ; on the other hand, those of Hlaphrus and the 
majority of the Harpalinz, in which the primitive quadrate 
head and short legs have been retained while the long 
cerci have become greatly reduced. 
