1905] THE EaGcs OF THE SCARLET WaTER-MITE. IOI 
where the eggs pressed against each other, slightly flattened facets 
were formed (fig. 1), a feature noticeable in many other eggs, 
especially the eggs of certain fishes. In diameter each egg was 
about ;$, of an inch, or slightly larger than the mites’ eggs de- 
scribed by Claparéde, which were about ;4, of an inch in long 
diameter, the form being ellipsoidal in that case. Claparéde 
states that the eggs may be deposited at all times of the year*, 
but in the case of this Canadian Hydrachna the chief spawning 
period may be in the warmer summer months. 
When examined with a pocket lens, the bright red ball of 
yolk is seen to be surrounded by a dull whitish envelope, the 
external shell. Under a higher power, say 200 diameters, the red 
mass or vitelline globe, which is very opaque and dense, is en- 
closed by a thin skin or layer (fig. 1, 4) outside of which is the 
extremely thick external capsule or shell (fig. 1, c), This external 
shell, which I distinguish as the chorion, is either of great thick-. 
ness or a wide space separates it from the vitelline globe inside. 
In the hen’s egg the yellow vitelline ball is separated by a wide 
albumen-filled space from the outer white shell; but the shell itself 
is thin. Claparéde, inthe mites’ eggs which he describes, speaks of 
a space between the outer shell (his ‘‘ Schale” or ‘‘ Dotterhaut ”) 
and the contents inside; but, while he describes a thin layer 
” 
around the dense yolk-ball, the ‘‘ Keim-haut,” which is not really 
an ege-membrane at all, but a thin layer of germinal protoplasm, 
he mentions a third layer or skin, which he distinguishes as the 
‘* Zwischenhaut”’ ; and the vitelline ball is thus surrounded by 
three membranes. The outermost is a true chorion produced not 
by the yolk but by the epithelial cells of the oviduct, whereas a 
vitelline membrane or zonaradiata is always a product of the vitellus 
or egg itself. The chorion in the egg of Hydrachnais hard like horn 
and extremely granular in appearance, as though studded all over 
with grains or minute papille, each papilla, under a high power, 
. apparently exhibiting a puncture (fig. 2). _I tried various experi- 
ments in order to prove the existence of pores or canals in the 
shell, and of a wide space separating the shell from the yolk-ball 
inside. I subjected some eggs to great pressure under a cover 
* Op. cit., p. 451. 
