Lower Animals. 
1884.] 
2 77 
been bitten in the foot by a Tegenaria, amputated the enve- 
nomed member. 
Such cases of self-mutilation have been of late carefully 
studied by M. Leon Fredericq, especially as regards crabs. 
The results of his interesting observations have been made 
known in the “ Archives deZoologie Experimental, ” and in 
the “ Naturforscher.” 
He establishes, in the first place, that this process of mu- 
tilation is performed in the same manner on any leg, and, if 
it so happen, on every leg of one and the same animal in 
succession. The fraCture always takes place at one and the 
same part of the leg, in the continuity of the second joint, 
counting from the body, and leaves a rounded sharply-marked 
surface. This part is by no means characterised by unusual 
fragility. On the contrary, the leg of a dead crab possesses 
a great power of resistance, and bears a strain of several 
pounds without giving way. When actually broken it has 
an uneven surface, and the fraCture scarcely ever occurs in 
the continuity of the second joint. 
Experiments on the conditions in which the living animal 
throws off its leg prove that a fraCture is effected at the 
point in question by an energetic muscular contraction. 
The limb is invariably broken off if the nerve of sensation 
of the leg is strongly irritated. M. Fredericq found it pos- 
sible to induce self-amputation by applying a mechanical 
irritation to the sentient nerve of the leg at a more peripheric 
point. If this irritation is less marked, as for instance by 
gradual section of the leg, the animal does not reaCt by self- 
amputation. If, however, the end of the nerve thus exposed 
is moistened with alcohol, the crab replies to this chemical 
irritation by an amputation at the second joint. If the leg 
is heated the thermic irritation at once produces a fraCture 
at the same place. It was also found very easy to bring on 
amputation by applying electricity to the nerve. These last 
experiments permitted a measurement of the time. It was 
found that the interval between the irritation of the nerve 
and the rupture of the leg is very variable, ranging from a 
few hundredth parts of a second to an entire second, and 
even more. 
After these experiments had sufficiently proved that the 
amputation of the legs in crabs is a reflex process, M. Fre- 
dericq endeavoured to ascertain the nerve-centre which is 
the seat of the mechanism. The removal of the ganglia of 
the throat had no influence on the phenomenon. But if the 
ventral ganglia were destroyed the reflex mechanism was 
annulled. The entire leg might then be cut off without 
