perfect State of Prosopistoma punctifrons. 81 
The first five segments of the perfect insect represent those 
which, more or less soldered together, occupy in the ventral 
surface of the nymph all the space included between the last 
pair of feet and the lower part of the ventral apertures (fig. 4) ; 
the sixth is formed by that to the dorsal surface of which the 
extremity of the carapace is soldered; the seventh and eighth 
correspond to the first two free segments of the abdominal 
region of the nymph; the ninth has nearly the same form in 
these two states of Prosopistoma ; for in both cases it performs 
nearly the same part, namely the protection of the last seg- 
ment. The latter in the subimago is composed of a dorsal 
plate, which is homologous with the dorsal surface of the same 
segment in the aquatic insect, and of two atrophied plates 
which, placed over the sete, represent the two plates of the 
ventral surface of this tenth segment in the larval and 
nymphal forms of the Prosopistoma. 'The mobility of these 
inferior plates is far from being so great in the perfect insect, 
seeing that the setee have lost the faculty of withdrawing 
themselves completely into the interior of the penultimate 
segment. We have observed only four pairs of stigmata, 
placed on the sides of the dorsal surface of the third, fourth, 
fifth, and sixth segments ; we believe, although we have not 
been able to ascertain it de visu, that there are also stigmata 
upon the second segment. 
It remains for us to add to what has just been said on the 
form of the various regions of the body ,that all the integu- 
ments are covered with simple hairs, more or less closely 
adpressed to each other according to the parts examined ; these 
hairs are also abundant upon the surface of the appendicular 
organs. 
We now proceed to examine the organs of the senses, the 
legs, the wings, and the set, which we have hitherto passed 
over. 
Antenne.—In the nymph the organs of touch are formed of 
six joints, which are unequai but have nearly the same form ; 
this is no longer the case in the perfect state (fig. 13), in which 
the antennee have only two very unequal joints and a flagellum. 
The basal jomt, of a cylindrical form, is rather short; the 
second, on the contrary, is at least three times as long, inflated 
in the middle, and attenuated at the apex; both these joints 
are of a brown colour, and are also covered with a great 
abundance of hairs. 
The flagellum, which is inserted at the extremity of the 
second joint, is of itself as long as the rest of the antenna; it 
is very slender; and its tegumentary envelope, which is desti- 
tute of hairs, presents a very pale brown colour. 
