
54 THE NORTHERN MICROSCOPIST. 

absent on the intermediate pair. The sete are nearly equal in” 
length ; these appendages, as well as the segments of which they 
are composed, being usually much longer in the male than in the - 
female. The male forceps are either jointless, two-jointed, or 
tipped with a minute sharp process. The type of the genus is” 
Ceenis macrura, which makes its appearance as an imago between 
May and September ; in summer the early morning and the cool 
evening being preferred by the insect for its final ecdysis. The | 
Rey. A. E, Eaton, our greatest authority upon this family, has found 
the subimagines of this genus waiting at half-past five in the morn- ~ 
ing in June for the sun to dry the dew upon their wings before 
attempting their last moult. Spiders’ webs and newly-painted 
wood in the neighbourhood of gentle streams and quiet lakes and | 
ponds should be examined for specimens when they are not found 
in flight. Although not so common in the British Isles as the _ 
genus Cloéon, Czenis is sometimes found flying in swarms at the ~ 
beginning and end of summer. Dr. Hagen describes the English — 
species as appearing in such numbers in Prussia that objects 
near the water have been covered by them to the depth of an inch, ~ 
which, considering the small size of these insects, would necessitate 
many layers placed one above another ; whilst, in the “ Curische 
Wehrung,” the pigs are sometimes fattened upon them. The 
length of the body of the mature female seldom exceeds one-fourth — 
of an inch, the male being usually much smaller. 
The typical attitude that the subimago assumes during repose is : 
with the wings widely expanded, the fore-legs on the ground, and 
the caudal setee nearly parallel. 
The winged Czenis lives an exceptionally short time for even this : 
short-lived family. Its eggs are soon deposited, and the object of — 
its aérial life being accomplished, exhausted it expires. ‘The chief 
characteristic of an Ephemeridous egg is, that the germinal matter 
is segregated in one part, the remaining portion containing some 
kind of formative material, serving, no doubt, as a store for the 
further development of the embryo until it becomes capable of © 
leading an independent life. In the eggs of some of the genera _ 
there is a constriction between these two portions, more effectually 
separating them. This is the case in the eggs of Cloéon and 
Ephemerella. In other cases the germinal portion assumes the 
form of a crescentic protuberance from the rest, and this appears — 
to be its character in the genus Czenis. The eggs having been 
laid in a cluster on the surface of the water, they sink to the 
bottom, where they may either be eaten by some hungry trout or | 
other fish, or lie in unobserved security for a few weeks until they — 
become hatched. In the struggle for existence these insects often — 
have a hard time, for no sooner does the larva issue from the egg — 
than other larvee, of a larger growth, are waiting to attack it; and 
