478 SIR J. LUBBOCK ON THE DEVELOPMENT 
Hitherto all the specimens of the species have resembled one another; but about this 
period of development the external sexual characters of the males begin to show them- 
selves. Between the two large original eyes we now see indications of a second pair, the 
rudiments of the two great pillared eyes. In the cast skin we may see that the chiti- 
nous head-covering has here undergone a change. The skin is neither divided into the 
more or less regularly hexagonal facets of the original eye, nor does it present the irre- 
gular polygons which mark the upper part of the head; on the contrary, it is marked by 
a great number of small wedge-shaped dots, which divide it into minute fields, the future 
facets. These incipient eyes lie close to the others, occupy already a considerable part 
of the top of the head, and are of an elliptic form. | 
The second character of the male sex occurs on the underside of the penultimate ab- 
dominal segment, the outline of which now presents two very slight projections, which 
are of importance only as indications of future changes. The females do not appear to 
present the slightest trace either of these processes or of the pillared eyes. 
In the female, the commencement of the ovaries may now be observed, in the form of 
two cylindrical organs, one on each side of the abdomen. They consist of a central tube 
with short lateral lobules. 
Nineteenth State. 
. The wing-cases now cover about half of the second abdominal segment, and the insect 
is about $ of an inch in length. The antennæ and caudal appendages have again in- 
creased in length and in the number of the segments. 
The pillared eyes are somewhat more developed, but the facets are still indicated only 
by the arrangement of the dots. They are about +2, of an inch in diameter, which is 
half that of the other eyes. | 
The anterior plate of the anterior branchia is somewhat longer than before, but there 
is no great alteration. 
The small projections on the underside of the penultimate abdominal segment are 
rather more developed, but there is no great change in them. 
The rudimentary ovaries are somewhat more developed. 
Twentieth State. 
In this stage, which is the last passed under water, the rudimentary wings cover half 
of the third abdominal segment, or, in some cases, the whole. The facets of the “ pi 
eyes,” which are characteristic of the male, are still indicated by dots; the facets of the 
ordinary eyes seemed to me to be more sharply defined than before. 
The anterior gills are but little altered. 
The antennæ are now far longer than they will be in the next state. This is interest- 
ing, as showing that the changes which have taken place in them are not mere stage 
in the development of the perfect form, but are adapted for some special object, which 
we have not yet determined. It may be thought that long antenna, like those of the 
full-grown larva, would be an encumbrance to flight, and that for this reason they are 
shortened in the imago; but, on the other hand, it might be said with an equal appe?" 
