NEUROFPTERA.—PERLID&. 93 
enclosed in a case, and in general form resembling the imago, except 
in wanting wings ; whilst the pupa is active, having a still greater re- 
semblance to the imago, possessing the four rudimental wing-cases. 
In a memoir published by Goeze in Der Naturforscher, st. iii. so 
long ago as 1774, a figure of the pupa of Perla bicaudata was given, 
answering to this description ; and specimens of the pupee are pre- 
served in the Linnzan collection. I likewise possess several (_ig.60. 8.), 
as well as the exuvie cast on the insect’s arrival at the perfect state, and 
which are found attached to plants, &c., in the vicinity of the water 
in which the larvae and pupe have resided. Dr. Suckow has also (in 
a memoir written with the view to prove that the Semblis [ Perla] bi- 
caudata, and Semblis [Sialis] lutaria belonged to different genera, as, 
indeed, they had long been considered by Latreille, and published in 
the Zeitschrift fiir die Organische Physik) described the Perla bi- 
caudata in its various states. More recently Mr. Newman has given 
a sketch of the larva of P. bicaudata (#int. Mag. vol.i. pl. 3. f. 10); 
and M. Pictet has published two memoirs, detailing the history of 
various species of Perla ‘and Nemoura, agreeing with the character 
given above. These larve prefer the most rapid parts of streams: 
they crawl about slowly, preferring to remain stationary under stones ; 
they are carnivorous ; they shed their skins several times (at least, in 
Nemoura) ; and they generally crawl out of the water when about to 
assume the perfect state. M.Pictet has described these larve in 
detail ; it will, however, be sufficient to notice that, unlike the imago, 
the mandibles in the larve of Perla (ig. 60. 9.) are robust and toothed, 
as well as the maxille ( fig. 60.10.); the eyes are prominent and la- 
teral, and in the place of ocelli I observe three black dots between the 
eyes, which M. Pictet has not described. The tarsi in the pupz of Perla 
(fig. 60. 11.) appear to me to be composed of three joints, the two basal 
ones being very minute, the first almost hidden from view; in the 
larvee of Nemoura the tarsi are 2-jointed. M. Pictet has described 
two singular modifications in the respiratory organs of these insects. 
In the larve of the large species composing the genus Perla, as re- 
stricted in my Generic Synopsis, each of the three thoracic segments 
is furnished with a pair of tufts of short external filaments, each tuft 
being composed of three distinct pencils, each having a distinct 
origin (fig. 60. 12.). : 
In the Perla virescens Pictet (evidently a Chloroperla Mewm.), and 
in Perla nigra Pictet (which will probably form a different subgenus, 
c 4 
