404 
CHIYOMATSU ISHIKAWA. 
these two membranes a certain quantity of clear liquid is found, 
which coagulates and becomes finely granular in alcohol. 
The primary egg-membrane always shows a granular reticu- 
lated appearance, with oval or round interstices. These are 
caused by the yolk-spheres, on which the membrane closely 
adheres at the beginning, and is not to be mistaken for the 
cellular markings found in insect ova. The secondary egg- 
membrane is perfectly structureless, and is thicker and firmer 
than the primary. Both egg-membranes are at first extremely 
elastic, as is seen in the exit of an egg through the narrow 
opening of the oviduct. 
A number of different observers have spoken of the existence 
of two membranes on the eggs of Decapods. Rathke (-|) and 
Reichenbach (^ 7 ) have found them in the eggs of Astacus 
fluviatilis, Bobretzky in Palsemon, Erdle in Homarus, 
and Dohrn in Scyllarus arctus f 2 -^ 1 ), Palinurus vul- 
garis ( 2 T 5 f), and in Portunus (Vr)- 
It remains now for me to consider very shortly the germinal 
vesicle and its final fate. The germinal vesicle presents one or 
two or rarely three germinal dots in younger eggs ; but in those 
eggs which are grown to a considerable size, and which are 
found in the vitellogen, are always provided with a single dot. 
It is thus distinguished from the ova of Astacus, in which 
Lereboullet, Waldeyer (\ 5 ), Huxley (^-§-2-), and others have 
found many germinal dots, and from that of Eupagurus, where 
Mayer has found only a single dot in all the stages of the 
development of the egg. It does not grow, as I have already 
mentioned, as rapidly as the egg, and when the egg is 
quite ripe the germinal vesicle disappears. I have made hun- 
dreds of sections of the ripe ovary, and have always found 
the ripened eggs devoid of nucleus, while the younger ones 
show it very plainly. No nuclear structure can also be seen 
in freshly-laid eggs. Mayer speaks of it so explicitly in the 
egg of Eupagurus that I will quote his own words here (-i-f-2) : — 
“ Nach einiger Zeit, und zwar noch wahrend das Ei im Ova- 
rium befindlich, verschwindet — wie dies auch schon Rathke 
von Astacus angibt — das Keimblaschen, so dass die frisch 
