Tae NortHern Muicroscoptst. 


No. 1. JANUARY. 1882. 


THE EPHEMERID&, OR MAY-FLIES. 
By W. BLACKBURN. 
Concluded from page 290. . 
HE circulation of the blood and pulsation of the dorsal vessel 
are very well seen in these larvze, on account of their transparence. 
The dorsal vessel extends nearly the whole length of the body, and 
is furnished at regular intervals with valves, dividing it into cham- 
bers, one chamber to each segment of the body, through which the 
blood moves towards the head. At the posterior extremity of 
each chamber, a central valve allows the blood to enter from the 
adjoining chamber, while external openings receive the blood from 
the interspaces of the surrounding tissues. The dorsal vessel 
divides in the head into two branches, through which the blood 
flows into the open cavities of the body. ‘The corpuscles of the 
blood, by which this motion is observed, are oblong, ‘somewhat 
“ oat-shaped,” when viewed in one direction, but approaching more 
to the circular form when seen in another direction. 
Sir John Lubbock traced the life-history of a Cloéon from the 
egg to the imago, and we learn much concerning the growth and 
development of the Ephemeridze from his’ instructive record. 
Cloéon is a small British genus, very common in still water, ‘that 
makes its appearance as an imago from May to October. Fig. 61. 
When it escapes from the egg, it is about } of an inch in length. 
Its antennz are ; of an inch in length, and consist of thirteen seg- 
ments. It has two tails of nineteen segments each: It has neither 
gills, spiracles, nor trachez. Respiration must, therefore, be effected 
through the integument. It is provided from the first with six 
legs, in which the tibize and tarsi are firmly united. ‘The tarsi are 
jointless, and terminate in a single claw, the same as in the other 
genera... There are five eye spots visible, all similar to each other. 
Swimming is effected by jerks of the abdomen upwards and down- 
wards. In this motion the tails assist. When any small creature 
comes in contact with Cloéon, the tails are immediately advanced in 

