118 Victor EK. Emmel. 
through the ventro-anterior region of the breaking joint, and is 
inserted upon the inner wall of the basipodite. It functions as a 
flexor. This muscle persists throughout the first four larval stages 
of the lobster’s development. During the fifth stage, however, it 
begins to degenerate, and at the sixth stage the former muscle is 
represented by a mere bundle of connective tissue (Fig. 6, ct.), con- 
taining a few remnants of the degenerating muscle fibers (md). 
It is interesting to note that the stage of the lobster’s development 
at which the degeneration of this muscle occurs is not only the one 
just preceding the stage in which the asymmetrical differentiation 
of the chela first becomes evident, but, as the writer (’08) has previ- 
ously shown, it is also the stage after which the asymmetrical differ- 
entiation of the chelze can no longer be experimentally controlled. 
The discovery of this muscle introduces a new fact to be taken into 
account in the question of the morphological significance of the 
breaking joint. Andrews (’90) maintains that the origin of the 
breaking joint may be ‘“‘explained as a modification of a former free 
joint” (p. 142). On the other hand Reed (’04) concludes, from a 
comparative study of the crustacean limb, that it ‘“‘seems, therefore, 
erroneous to state that the breaking joint corresponds to the lost joint” 
(p. 311). Without entering into a discussion of this question, it 
may be observed that the existence of a muscle in the chela of the 
larval lobster which crosses the breaking joint and is attached to its 
two adjacent segments, seems a strong point in favor of Andrew’s 
conclusion. 
d. Autotomy.—The process of autotomy or defensive mutilation 
among crustaceans has been fully described by Frederieq and Mor- 
gan. When the nerve within the chela is experimentally stimulated 
a vigorous contraction occurs in the muscles of the basal segment, 
followed by a sudden snapping off of the limb at the breaking joint, 
leaving the exposed surface of the stump as smooth.as if eut with a 
keen-edged knife. Regarding autotomy in the larval lobsters, I ean 
confirm Herrick’s observation that the “casting of the claw” does 
not occur before the fourth larval stage. In experiments with 
several hundreds of first, second, and third stage lobsters in which 
one or both chelee were removed, I have never observed the limb to 
