2 THE NORTHERN MICROSCOPIST. 
front, as if for the purposes of defence or sensation. The larger 
larvee, such as Ephemera, never advance the tails in this manner. 

Fig. I, Female Imago. x 21%. 
In from two to three days Cloéon casts its first skin. In so 
doing, it does not, as is usually the case with these larva, split the 
skin of the thorax, but extricates itself through the top of the head. 
The orifice is very small, and the skin left is very perfect. After 
moulting, the length of the body is found to be ;sth longer than at 
birth, The antennz and tails are also slightly longer. The 
antennee possess the same number of joints as before, and the tails 
one more joint, the extra length being principally found in the first 
segment of the tails, and the third segment of the antenne. The 
posterior angles of the second to the sixth abdominal segments are 
slightly produced, indicative of the position of the subsequent 
gills. A minute knob appears between the two tails, the rudiment 
of the middle tail. 
In a few days the second moult takes place. The antennz are 
now found to have increased in length, and to consist of two more 
q 
