112 Victor E. Emmel. 
facilitate a comparative study, the specimens were all cut in a nearly 
constant plane. In addition to this series, sections of the regener- 
ating limbs of older lobsters were also studied. 
The material used was fixed in a saturated 35 per cent alcoholic 
solution of corrosive sublimate. Several other fixing agents were 
tried, but all solutions containing acids proved unsatisfactory on 
account of their injurious reaction with the chitin and salts of the 
exoskeleton. The nuclear and cytoplasmic stains employed were 
alum heemotoxylin, Heidenhain’s iron-alum-hematoxylin, Congo-red, 
eosin, and Mallory’s connective tissue stain. 
III. AnaTomMiIcaL STRUCTURE OF THE CHELA. 
1. Segments, Muscles, and Joints.—The following account is con- 
fined to those structural characteristics of the limb which are essential 
for the subsequent description of its regeneration. 
The chela of the lobster is composed of six segments (Fig. 37). 
Proceeding in a disto-proximal direction these segments are known 
successively as a dactylopodite or dactyl (d), propodite (p), carpopo- 
dite (c), meropodite or meros (m), ischipododite (7), and basipodite 
(bs). A seventh basal segment not involved in the present study is 
the coxopodite. The index is the distal part of the propodite which 
opposes the dactyl and forms one jaw of the large claw. All of these 
seven segments are united to each other by flexible joints with the 
exception of the last two,—the ischiopodite and basipodite. These 
are fused together into an immovable joint or “breaking-joint,” a 
structure especially adapted to the process of autotomy. ach joint 
is like a hinge, articulating at two points and permitting only a 
simple flexion and extension of the segment. The musculature of 
the chela consists of a pair of opposing muscles for each of the 
segments with the exception of ischiopodite (Fig. 37). The pair 
of muscles in any given segment is attached proximally to the chitin 
of the proximal region of the segment. Distally the converging 
muscle bundles are attached to a chitinous plate or ingrowth of the 
exoskeleton of the next segment distad. The origin and insertion 
of the extensor and flexor are on opposite sides of the joint. In 
each of the first three pairs of muscles, the flexor is larger than the 
opposing extensor. 
