NOTES ON THE EPHEMERIDA. 459 
divided up into squares, each square being covered with minute 
hairs. 
The eggs of Mayflies are laid on the surface of the water, 
the whole quantity being deposited at the same time. The eggs, 
being heavier than the water, sink immediately. In Hphemera 
vulgata the eggs are described by Dr. H. Grenacher as possessing 
striated caps of reddish brown colour, which invest both poles of 
the egg. A mushroom-shaped stalk serves as a base and springs 
directly from the end of the egg. This is of firmer consistence 
than the striated part, whose numerous and close-set fibres 
radiate regularly from it. The fibres had previously been de- 
scribed by Leuckart as bundles of spermatozoa. No definite 


information as to the functions of these striated ege-caps has 
been obtained. Grenacher has also described what appear to be 
long anchoring threads attached to the eggs of H. vulgata. From 
eight to twelve of these are fixed to a zone which encircles the 
egg transversely towards one end. EKach thread bears a small 
knob at its free end, and these knobs apparently become en- 
tangled at the bottom of the stream and moor the egas.* 
The larve of Mayflies may be conveniently divided into three 
groups, namely: 1, burrowing; 2, swimming ; and 3, creeping 
larve. The body of a larva is composed of fourteen segments, 
* Miall, ‘ Natural History of Aquatic Insects.’ 
