A NYMPH OF THE GENUS CANIS. fs 

if, in spite of its aquatic foes, it succeed in arriving at maturity, the 
dragon-fly and other predaceous insects and numberless small 
birds are on the watch for the dainty morsel ; so that if it were not 
for the great number of eggs that are laid, the Ephemeridz would 
soon become extinct. 
When the larva of this genus has escaped from the egg, its 
attempts at swimming, which are somewhat clumsy, are made in | 
a wriggling manner, the abdomen being moved rapidly from side 
to side, in order to propel the body slowly forward. This being 
the usual mode of motion in swimming, it is occasionally varied 
by the adoption of a vertical motion, still performed in a wriggling 
fashion, and giving the larva the appearance of having some diffi- 
culty in making its way through the water. The same motions are 
observed when the larva has become a nymph by being sufficiently 
matured to have acquired rudimentary wing-cases, As all the 
characteristics of the insect, in its aquatic state, do not appear 
until the elements of the wings are present, it is more convenient 
to describe the nymph than the less developed larva. 
The nymphs of this genus burrow in the mud or hide under the 
stones of the water they frequent, for which reason they are rather 
difficult to find. ‘They are either unarmed, in which case they are 
provided with the usual ocelli, three in number, on the forehead ; 
or, in place of the ocelli, they are furnished with three short conical 
horns, which occupy the same position on the forehead that the 
ocelli do in the unarmed species. ‘The unarmed nymphs are 
represented by the type of the genus, Cenzs macrura (Stephens ), 
in which the legs have the femora broad and strong, the tibize have 
their tips produced obliquely inwards and terminated by a bristle, 
and the claws are long and formidable. ‘The armed nymphs are 
represented by the species Cenzs luctuosa (fictet), in which the 
femora are more slender, and the tibia and tarsi are more ciliated. 
All the English species have the lateral edges of the posterior ab- 
dominal segments considerably produced and terminated in the 
form of a bristle; of the ten segments of the abdomen, the seventh 
and eighth are longer than the rest. The mandibles are well de- 
fined. ‘The inner edge is extended into a molary plate, the outer 
anterior edge is furnished with two stout spinous processes, well 
adapted for prehension. Both the maxillary and labial palpi are 
three-jointed ; of the former the second joint is the shortest, the 
first and third being nearly equal in length; of the latter the first 
joint is much the largest. The segments of the antennz and tails 
are rather long in this genus, and are furnished at the joinings with 
a few short hairs. ‘The second segment of the antenna is much 
longer than the first. The tails are comparatively short in the 
nymph and subimago, and this character is generally preserved in 
the female imago, but in the male imago these appendages appear 

