THE AMERICAN LOBSTER. 
147 
each other. The pollux is depressed, so that when the claw is closed it falls almost 
exactly midway between the normal and first superadded digit. The fission is marked 
on the upper surface by a distinct groove. The total length of the propodus is about 
2£ inches (62 mm.), so that the lobster was not in all probability over 6 inches long. 
The size of this claw as compared with the basal joints of the limb suggests that it 
has been lately regenerated, and it is unfortunate that this interesting point can not 
be determined with certainty. 
In fig. 196 a similar monstrosity is seen in the dactyl of the cutting-claw. Here 
the bifurcating branch is near the apex. Each prong is furnished with teeth on the 
inner side. A trimerous dactyl (fig. 195), one division of which is independent, in 
the second or third pereiopod presents precisely the same relations which occur in the 
first pereiopod (fig. 193), and probably they have been produced in the same way. 
What is now most needed in clearing up questions in the interpretation of 
deformities in crustacean appendages is to watch the molting of the animals and to 
measure and record the change which occurs in the malformed individual at each stage 
of growth. The abnormal developments seen in figs. 189-193 probably represent a series 
of changes such as ordinarily occur in the same individual. What the course of events 
really is between the conditions represented by figs. 193, 192 is not so clear. 
While the true duplication, or even triplication, of limbs or parts of limbs is rare 
in Crustacea, it is occasionally met with; but it is an important fact, which Bateson 
has emphasized, that “in arthropods and vertebrates such a phenomenon as the 
representation of one of the appendages by two identical appendages standing in 
succession is unknown. No right arm is ever succeeded on the same side of the body 
by another arm properly formed as a right, and no crustacean has two right legs in 
succession where one should be.” 1 
In the American Museum of Natural History, in New York, there is a specimen 
of a lobster in which the right cutting-claw is perfectly duplicated from the carpus 
or fifth joint. I was recently enabled to examine this interesting specimen and to 
make some drawings of it, which are given in cuts 16, 17, plate E. 
The two cutting-claws resemble each other very closely in every detail and are 
of almost exactly the same size, but each is relatively smaller than normal. The 
measurements of each cutting-claw are as follows : 
Right cutting-claws (abnormal) : Inches. 
Length of propodi 3|- 
Greatest breadth of propodi If 
Left crushing-claw (normal) : 
Length of propodus ; 5 
Greatest breadth of propodus 2 
In the primary cutting-claw the dactyl closes normally on the propodus-; in the 
superadded claw ($. C.) it is bent upward out of line with the cutting edge of the 
latter. The symmetry of the two claws extends, with few exceptions, to the spines 
upon their cutting edges and on the inner margins of the propodi. The carpus of 
the limb is apparently single, but it has duplicated spines, and a deep groove at its 
peripheral end shows that it is virtually double. The carpus and meros have been 
twisted through an angle of 90°, so that their posterior surfaces face upward. 
This specimen was obtained some years ago from a marketman in New York City. 
Materials for the study of variation, p. 539, 
