234 Proceedings of the Koyal Society of Edinburgh. [Sess. 
The benefits accruing from autotomy being so evident, it remains, 
therefore, to find by comparative study how the process may have been 
evolved, and what are its essential features. Examination of different 
species of decapods by different persons has produced a good deal of 
literature on the subject. It is very noticeable, too, how each author con- 
tradicts on fundamental points those who have gone before him, simply 
because he has studied a different animal, and because a particular feature 
of the process in his type may be more developed than others, and so 
overshadow them. 
The older biologists {e.g. Reaumur (3), 1712) noticed that if a crab’s 
leg were cut off outside the breaking-plane at the base, it was subsequently 
thrown off by the animal at the breaking-plane. The same was recorded 
by many observers of the first part of the nineteenth century, including 
Faxon (4), McCulloch (5), and Heinehen (6), but it was only when 
Fredericq (2) took up the question at the end of the ’eighties that new 
light was thrown on the subject. The result of his work was that in 
Garcinus moenas autotomy was shown to be the result of reflex contrac- 
tion of a definite muscle which came to be called the “ autotom iste ” or 
“ Brechmuskel.” The reflex-arc involved had its centre in the ganglionic 
mass of the thorax, and acted independently of the cephalic ganglia. The 
necessary stimulation could be provided by burning, cutting, crushing, or 
electrically stimulating any distal segment of the leg except the last one. 
Autotomy could also be produced by central stimulation. 
Fredericq’s conclusions regarding the reflex in Garcinus have been 
applied to other species without allowance having been made for differences 
of form and conditions, and a certain amount of confusion has arisen. 
Among recent writers are Morgan (1), Reed (7), Steele (8), Przibram (9), 
Pieron (10), and Drzewina (11). The results of these workers will be 
discussed under the parts of this paper dealing with the special animals on 
which the work was done. 
Section I. MACRURA. 
Suborder Nat anti A. 
The Prawn. 
Of this group I have examined only one species — the prawn, Leander 
squilla (Lin.). This animal, in relation to its size, is one of the fast- 
swimming decapods. Its tail fin and abdominal muscles are well developed, 
and by violent contractions of the latter it makes rapid backward move- 
ment. The walking-legs are very like those of the lobster, but there are 
