COXJUGATIOX IX THE CRAYFISH, CAMBARUS AFFIXIS 257 
thrust down and forward, held stiff by the fifth leg, and at the 
same time the long chelate legs straightened themselves out. This 
last action, with the others, necessarily pushed the body of the 
male as one mass up away from the female. Had the body been 
hooked it would have acted as a lever about the hook as a ful- 
crum and thus the rising up of the anterior end of the body would 
have made the posterior end move down ; this in turn would have 
thrust the tips of the stylets forward as well as downward and 
so have helped in the entrance. 
Diagrammatically expressed, the normal use of the hooks is to 
hold the middle of the male firm so thatthe body of the male can 
move on the hook region as a see-saw. When the chelae shove up the 
head endof thesee-sawtheotherendgoesdown. The stylets being 
held firmly at an angle of 45 degrees tend to push against the 
ventral surface of the female both downward and forward. The 
strength of the chelae is utilized as an aid to the entrance of the 
tips of the stylets into the sperm-pocket. All the most powerful 
muscles of the male seem necessary for sperm transfer. 
When the hooks were not there and there seemed no way to 
hold the body of the male firmly to the female at the middle of 
the length of the see-saw, then the force of the chelae raised the 
male away from any possibility of getting the stylets to the an- 
nulus. 
The absence of the hooks thus led to a separation of the male 
and female thoracic surfaces, and nevertheless the stylets high in 
the water above the annulus were then seen to be quickly jerked 
forward several times, as if to enter the annulus. But the male 
next acted as if missing the usual response; he endeavored to 
hold the female tightly with his claws and legs that encompassed 
her thorax; and after some efforts turned the small antennae 
directly down and backward under his head as if in search of 
impressions. The third maxilliped was also used in rapid palpation 
of the bases of the female legs. 
Another male with no hooks after such a first trial with the 
right leg crossed stood up an inch from the female and substituted 
the left leg and then went through the maximal contraction-phase 
