406 
CHIYOMATSU ISHIKAWA. 
morning, and is preceded by an exuviation, which usually occurs 
during the night. The mode of egg-laying seems to be essen- 
tially the same as that described by Lereboullet, although, un- 
fortunately, I have not been able to get an access to his original 
description, an inconvenience which often happens to a natu- 
ralist working here. 
The prawn before the egg-laying is seen to be very uneasy 
(the uneasiness may, perhaps, be owing to the late exuviation), 
continually moving about until it finds a good resting place. 
It then bends its body downwards in the form of a fish-hook, 
and thus forms a sort of a pouch with its abdomen, the tail of 
the animal corresponding to the point of the hook. Into this 
pouch the eggs are laid. 
During the act of laying the thoracic legs are kept continually 
moving, the last pair seemingly assisting to drive the eggs 
downwards, while the swimmerets are seen to be in rapid 
motion. The abdominal segments from the first to the fifth 
are also seen to move rhythmically. 
The eggs in coming out of the oviduct become very much 
elongated, almost rod-like, and, outside of the body, seem to 
take their course along the median line until they reach the 
abdomen, where they stick to the swimmerets. As regards 
the position of the eggs in relation to the swimmerets, I have 
observed that those eggs which come out earlier are received 
by the anterior pairs, while the later ones are driven to the pos- 
terior by the last pair of thoracic legs. As soon as they leave 
the oviduct they become more spherical, until they take their 
characteristic ellipsoidal form. 
There seem to be various opinions as to the means of the 
fixation of the eggs to the hairs of the swimmerets. Accord- 
ing to Lereboullet, the soft skin of the abdomen of the mother 
crayfish (Astacus fluviatilis) secretes a liquid which gives 
origin to both the outer egg-membrane and to the substance 
binding the eggs to the swimmerets. Huxley in his Crayfish 
says (L 0 ) : "These as they leave the apertures of the oviducts, 
are coated with the viscid matter, which is easily drawn out 
into a short thread.” For my own part, I can say almost nothing 
