ON THE NORFOLK HESPERIA ALVEUS. 219 
very exiguous depth, and that the lens must reproduce both the 
accurate and the distorted aspects of the subject. On the other 
hand, it is claimed by the advocates of drawings from slides that 
their method gets rid of the distortion difficulty and reveals what 
the ‘master’s eye’ can see; but the matter under consideration 
seems to be one in which the assistance of the organ in question 
may very well be dispensed with; for it is certainly doubtful 
whether features which require the ‘master’s eye’ for their 
appreciation have any practical taxonomic value. One some- 
times meets with such a phrase as ‘‘ apprenticeship in the study 
of genitalia,” which would seem to imply that the composition 
of the posterior end of the lepidopterous body is something not 
to be comprehended by the average intellect; as a matter of fact 
the organs which furnish useful differential characters are so few 
in number, and the plan on which they are arranged is so simple, 
that all the preliminary knowledge necessary for their successful 
investigation may be obtained in an hour or so. Genitalic 
characters are of such evident utility that it would be a great pity 
if any should be dissuaded from the study of their real nature 
and taxonomic function as the result of the squabbles between 
the Big-enders and Little-enders as to whether the parts are to 
be examined in the lateral or in the ventro-cephalad aspect. 
No one familiar with the blackish-grey white-spotted upper- 
side of Hesperia malve would mistake it for H. alveus, with its 
nut-brown yellow-spotted upper surface, and it was precisely 
_ because the late Rev. T. H. Marsh did not know the former (a 
rare species in Norfolk), that he placed his Norfolk specimens of 
a Hesperia, which he captured whilst working the flowers of 
Pedicularis sylvatica for Macroglossa bombyliformis, in his collec- 
tion under the name of alveolus. Here they remained until they 
came under the notice of Basrett, who saw that they were not 
malve, and at length identified them as H. alveus. The latter 
belongs to a group of species which are most certainly determin- 
able by reference to the male genitalia. The clasp in the lateral 
aspect is about twice as long as wide, with the apex broadly 
rounded, almost in a semi-circle. At first it seemed reasonable 
to refer all specimens having a clasp-form falling within this 
definition to the same species; but M. Charles Oberthur, in the 
course of his studies, found himself able to separate the alveus of 
the mountains from the alveus of the plains, to which latter he 
gave the name armoricanus. The characters relied upon by M. 
Oberthur are found by Prof. Reverdin, as the result of most 
ample investigation, to be correlated with certain differences of 
degree in the male genitalia; differences which—as he puts it— 
are more or less marked, but constant. So little marked are 
these differences that they did not in the first instance appear to 
me to be greater than what one might reasonably expect to find 
amongst members of the same species ; and it remained for Prof. 
