253 
1914-15.] The Reflexes of Autotomy in Decapods. 
it cuts through tough material till it reaches the breaking-furrow, when it 
is stopped. There is thus a junction in the ring of calcified material at 
an angle to a line of radius (figs. 18 and 19). 
The physiological processes connected with autotomy in Brachyura 
have been studied principally by Fredericq and Demoor (13). The former 
used Carcinus moenas in his experiments, and the following are his 
findings : — 
(1) The leg of a dead crab resists a force of to 5 kgms. applied 
i 
Fig. 18. 
These figures show the structure of the basi-ischium in Cancer. 
B.p., breaking- plane ; l.e., long extensor ; a, joint in the lower ring (basium). 
along the axis of the leg, and when rupture takes place it occurs at the 
junction between body and first segment, leaving a large wound. 
(2) When a leg is injured the long extensor of the second segment con- 
tracts violently, and the leg is pulled upwards till its distal part reaches 
the overhanging carapace. The long extensor continues to contract, and 
the leg divides at the groove in the basi-ischium (the point of least 
resistance) (fig. 20). 
(3) In all cases Fredericq afilrms that a point d’appui is necessary, and 
this may be the overhanging carapace or the finger of the operator. 
(4) Integrity of the long extensor of the second limb-segment is the 
sole condition for the performance of autotomy, for breaking occurs when 
