284 E. A. ANDREWS 
till only half of the length of the radius remained in the 
groove, owing apparently to the elastic side walls of the groove 
shoving against the wedge (figs. 9, 10) as these walls are the closer 
together toward the tip of the stylet. 
By this mechanical means the piston might tend to recede, 
while the movements of the muscles of the abdomen might make 
the entire second stylet advance enough to shove the piston along 
the groove’again. We can easily pump the radius back and forth 
in the groove by moving the whole second stylet. The muscles 
of the abdomen make the slight twitching back and forth jerks 
of both first and second stylets above mentioned as tamping 
movements. Now after the first stylet, with the second locked 
to it, is introduced into the cavity of the annulus as far as possible, 
these movements of tamping, if they be continued, could not ad- 
vance the first stylet but may push the second further along the 
first and so cause the piston to act on the sperm. The dish-like 
head of the end of the radius (fig. 22) receives explanation upon 
the assumption that it is useful in shoving the sperm along in the 
tubule, in fact, the solid bone-like piston with horny cupped tip 
provided with elastic flaring edge seems a remarkably well made 
apparatus for pushing liquid along in a tube that it fits so well. 
Some such piston movements might be expected from the state- 
ments of Coste (C. R. 46, 1858), that Gerbe in his laboratory 
saw the male Astacus apply the foliacious part of the second sty- 
let to the first stylet and by reiterated back and forth motions 
during the passage of sperm, keep as he thought, the trough of the 
first stylet free from sperm ‘that might harden there else. Schil- 
linger, states that the second stylet is used to push the sperma- 
tophores out of the first stylet.’ 
The groove and its concealed inner part that forms the tubule 
are of course open to the water and if the sperm is to pass free 
from contact with the water to the cavity of the annulus the as- 
sumed piston movements of the radius may serve to clean out the 
tubule and fill it with harmless secretions. The source of such 
secretions may be surmised to be the glands in the tip of the pap- 
1 As reported by Ortmann in Bronn’s Klassen und Ordnungen. 
