61 



sheltered crevice in the rocks. The crab discarded the 

 imprisoned limb as a conscious effort in order to reach the 

 inviting shelter. This did not happen if the brain were 

 destroyed or if the commissures were cut (" psychic 

 autotomy "). 



It is difficult at the present juncture to accept 

 Pieron's explanation, as Mile. Drzewinaf has also per- 

 formed similar experiments with Grapsus, and has 

 obtained entirely different results. But so far as Cancer 

 is concerned, the " psychic autotomy " does not appear to 

 be present. 



It is not possible in the present state of our 

 knowledge to arrive at a definite conclusion with regard 

 to the full significance of the processes involved in 

 autotomy. But whatever may have been the lines along 

 which autotomy has been evolved, there is no doubt that 

 one of its most important objects is the prevention of 

 bleeding. If the arthrodial membrane between an 

 appendage and the body be cut, the crab will probably 

 bleed to death, and this appears to be one of the greatest 

 dangers with which the animal has to contend. The 

 limbs, on account of their position and size, are 

 continually in danger of being torn or crushed. If the 

 limb were seriously injured, and autotomy did not take 

 place, the crab would bleed to death, because the wounded 

 surface would probably be too large to allow coagulation 

 to take place. This difficulty is surmounted by the limb 

 being thrown off at the fracture plane, across which, as 

 we have already seen, a membrane is stretched. This 

 membrane is perforated by a small foramen through 

 which pass the nerve and blood streams connecting the 

 proximal and distal parts of the appendage. Over this 

 foramen a clot may readily be formed, and thus the 

 excessive bleeding may be prevented. 



t Drzewina, A. C.R. Soc. Biol., T. LXIII (1907), Nos. 33 and 34. 



