82 
Proceedings of the Pojal Society of Edinburgh. [Sess. 
under experimental conditions, many hundreds regenerating in the natural 
habitat were examined. These were taken in the trawl, collected on the 
shore, or captured by creels at different seasons of the year. Crabs re- 
generating in the common tanks at the laboratory were also continually 
watched, and it was in these that many of the processes which occur at 
moulting were observed. 
Fixation of tissue at first gave difficulty, disintegration taking place 
when ordinary fluids were used. It was found that fixing solutions must 
be strong to give good results, and the greatest success was obtained by 
use of the following : — 
Pure formaline . . . . .25 per cent. 
Saturated solution of picric acid . 35 „ „ 
90 per cent, alcohol . . . . . 40 „ „ 
The whole crab was fixed, for it was found that parts of the body 
collapsed if removed. Tissues were decalcified in phloroglucin-nitric acid 
solution, then carefully orientated, and embedded in paraffin. Complete 
serial sections were cut and stained on the slide with hmmalum, and also 
with eosin as counter-stain. Certain parts of the tissue were reconstructed 
by ordinary methods after examination of the series. 
Observations. 
1. The Provisions for Loss of the Limb. — Blood circulation in a crus- 
tacean limb differs from that in the higher animals. Arteries bringing 
blood from the heart penetrate to the distal extremity and end there. 
There are no definite veins, and the fluid travels backwards in the shell- 
like limb, bathing the bands of muscle and connective tissues. If such 
a leg be crushed, broken open, or cut across, the animal runs a great risk 
of losing all its blood ; for, as an additional danger to its broad blood- 
channels, the crab has a hard integument which cannot contract to prevent 
haemorrhage. Both of the above factors would therefore tend to make 
fatal haemorrhage the common lot of the crab, but another process has been 
evolved to prevent this. This is the process of autotomy or self-amputa- 
tion. Autotomy is a reflex action resulting from nocuous stimulation of the 
nerve to the limb. Frederique (13) first pointed out that the contraction 
at the extensor muscle of the basi-ischium (second limb segment) and the 
contact of the leg with a point of resistance produced amputation at a 
preformed breaking plane or joint at the base of the limb. The references 
to autotomy in this paper are only made so that the regenerative process 
may be described ah initio, for this process virtually begins immediately 
