Hyatt.] 
278 
[October 19, 
Professor Hyatt showed a collection of distorted lobster’s claws 
in most of which extra growth had been produced by wounds and 
injuries received during the period of moulting. This extra 
growth in most cases wherever it occurred had resulted in the 
formation of two opposed but immovable sections, correct repro- 
ductions of the jaws formed by the regular growth of the two 
terminal joints of the large pair of legs in the lobster. These 
sections not only represented the jaws in form, but were furnished 
with teeth of the sharp spinous type, like those of the young. In 
four of these specimens out of twenty the movable section of the 
jaw had however been reproduced with a more or less perfect 
articulation, and had been evidently functionally useful. 
He drew from these facts the conclusion that during extra 
growth from the sub-terminal section, if the animal made an effort 
to use the false jaws thus produced, a movable section or jaw would 
be formed of greater or less perfection in proportion to the success 
of the effort. The reproduction of the original type of the jaw in 
these parts seemed to him a most complete illustration of Darwin’s 
law of Pan genesis, since the false jaws have the form of the true 
jaws, furnished with teeth in the form of sharp spines ; whereas, 
these same false jaws acquire, through use, an articulation 
and sometimes large, blunted teeth. The teeth of the former 
were similar to those of the jaw of the smaller claw, which are 
used for catching and holding live prey, and are sharp through- 
out life, and the teeth of the latter are similar to those of the 
large jaw, which are used for the rougher work of crushing, and 
become stouter and larger in the adults of Homarus Americanus. 
The theory of Pangenesis accounts for the similarity in shape 
and in the type of the teeth produced in the immovable jaws 
which grow out simply on account of the irritation produced by 
wounds, and use for the more or less perfect addition of the 
articulation at the base of one section and the stouter forms of 
the teeth, which are described above . 1 
1 See Faxon, On some Crustacean Deformities, Bull. Mus. Comp. Zool., vm, pp. 
257-274, pi. 1 and 2, in which this subject has been fully discussed, fora fuller account 
of such distorted appendages and distinctions to be made between those produced 
by wounds and those which might be considered congenital. 
