57 



seriously injured, the crab immediately throws off part of 

 the limb. The whole limb is not sacrificed. The self- 

 amputation always takes place along the thin groove 

 present on the basi-ischium representing the line of 

 separation between the basipodite and ischiopodite. This 

 groove, therefore, may be said to surround the fracture 

 plane (PI. II, fig. 12, f.p.). 



When autotomy has been effected, the fracture plane 

 is seen to be covered by a thin membrane, or diaphragm, 

 which is perforated, slightly below the centre, by a small 

 foramen. The blood flows out through this small opening, 

 but soon coagulates, forming a clot over the mouth of the 

 foramen and also on the outer surface of the diaphragm. 



The diaphragm with its outer coating of coagulated 

 blood assumes a dark brown colour in a few days, and 

 ultimately becomes quite black. This black coating is 

 worn away in course of time, and reveals a thin membrane 

 extending across the stump. 



Beneath the membrane a small papilla makes 

 its appearance, and marks the commencement of the 

 regeneration of the limb.* 



Conditions necessary for Autotomy. 



The successful performance of self-amputation in 

 Cancer depends upon several conditions, of which the most 

 important are discussed below. 



1. The crab must be healthy. 



This is a most important factor. Animals which are 

 in a diseased or weak condition, or which have been kept 

 out of water for a considerable time, and in which, as a 



* According to Williamson, the regeneration only takes place 

 when the crab is preparing for ecdysis. The limb does not attain 

 its full size at the first moult after regeneration. Two or three 

 moulting processes must take place before the limb attains its normal 

 size. 



