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E. A. ANDREWS 
the male are so thrust in, horizontally under the rim on the joint 
of the leg of the female, that any force that tends to push the 
ventral surfaces of the two animals apart will be resisted by the 
rim till it should break. If, however, the leg of the male be thrown 
out away from the side (raised up) the hook will be disengaged. 
The female is held much as a piece of ice by tongs that tighten 
as the weight increases, or as a stone lifted by hooks in holes in 
its sides with converging chains. 
That this use of the hooks is a necessary part of the conjugation 
in C. afhnis seems demonstrated by the result of removing the 
hooks. As they are but protrusions of the connective tissue and 
epidermis covered with hard shell they can be cut off without 
serious injury to the animal and the animal retains all its usual 
eagerness for conjugation. 
When normal males are kept with females there is usually a 
sign that conjugation has taken place in the presence of the sperm 
plug. But when eight males had one or both hooks removed and, 
after two to four day^, were given females no sperm plugs resulted. 
The cause of this apparent failure in spite of the fact that many of 
the males were seen to seize the females was made out by observing 
several of those with one or with no spurs. 
The male crayfish without any hooks seized the female eagerly, 
turned her, grasped her claws, raised and locked the stylets, 
crossed the fifth leg and made both the maximum contractions of 
the entire body and then six or seven quick thrusts of the stylets, 
just as if hooked to the female. That is, the phases of conjugation 
went on as usual; the hooking being absent, the next stage was 
carried on. But a halt came when it was found that the stylets 
had not entered the annulus. This entrance is a difficult act that 
usually requires repeated trials. In these crayfish with no hooks 
the maximum contraction resulted in the elevation of the male 
a half inch above the female. When the male had settled down 
close to the female as if to fasten the hooks he then passed to the 
state of violent contraction. The abdomen held by muscles 
formed one mass with the thorax, the tail was strongly apphed 
against the coiled up tail of the female, the anterior part of the 
male abdomen was bent downward so that the stylets were 
