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PACIFIC SCIENCE, Vol. II, July, 1948 
tion of descriptions of at least five distinct "self- 
mutilation mechanisms,” each different and only 
two being partly correct (MacCulloch, 1825; 
Fredericq, 1882, 1883; Demoor, 1891; Wiren, 
1896; and Paul, 1915 b). Space does not permit 
a review of the historically significant mech¬ 
anisms of self-mutilation; the reader is referred 
to Wood and Wood {op. cit.) for a synoptic 
resume. 
A knowledge of the morphological features 
of the appendages which are directly involved 
with self-amputation is a prerequisite for under¬ 
standing the mechanism for severance in P. cras- 
sipes. Figure 15 serves to illustrate these features 
which, with their descriptions, will clarify the 
mechanism in this species. 
i. 
Fig. 15. Autotomy in P. erassipes; A, the pereiopod 
in normal position; B, the limb has been elevated 
until processes X and Y become contiguous; C, further 
levation has resulted in severing the appendage at the 
fracture plane. B., basis; CO., coxa; F.P., fracture plane; 
I., ischium; X, protuberance on coxa; Y, protuberance 
on ischium. 
The coxa (Fig. 15, co.) is a short, stout 
cylinder articulating with the sternum and 
epimeron and moving in an anteroposterior di¬ 
rection. A process which extends distally on the 
posterior side (x) is important in autotomy. 
The basis (Fig. 15, B.) is an extremely short 
cylinder with a smaller diameter than the coxa. 
It articulates with the coxa and moves in a 
dorsoventral direction; the wide arthrodial 
membrane which connects the coxa and basis 
permits extensive movement. The basis, being 
narrow, slips in under the dorsal, distal edge of 
the coxa during extreme elevation, a condition 
essential for autotomy. The distal end of the 
basis is marked by a groove which encircles 
the appendage and separates the basis from the 
ischium, the two podomeres being fused. 
Inserting on the anterodorsal edge of the 
proximal rim of the basis is the long slender 
tendon from which the fibers of the anterior 
levator basis (autotomizer muscle) arise. The 
muscle has widely distributed origins: from 
the anterior surface of the endopleurite, from 
the endosternite, and a few fibers from the 
epimeron and the dorsal surface of the coxa 
(Fig. 16, A.L.B.). 
The ischium (Fig. 15,1.) is larger and wider 
than the basis with which it is immovably fused. 
On its dorsoposterior surface a protuberance 
(y), which is important in the mechanism of 
autotomy, extends medially toward the body. 
None of the more distal segments are necessary 
for autotomy because it will occur in a normal 
fashion when they are removed. 
The mechanism of autotomy set forth by 
Wood and Wood (1932 ) has been corroborated 
in all respects by this study on P. erassipes. Their 
observations on dead animals have been re¬ 
peated on this species and were found identical 
The rapidity with which the limb is autotomized 
makes it impossible to observe the process; 
therefore it is imperative that the observations 
be performed on a preserved specimen or on a 
complete appendage detached from the body 
with the autotomizer muscle intact. 
To disclose the autotomizer muscle, windows 
were cut in the dorsal side of the coxa and 
