572 Charles Zeleny 
glypha (up to 15 mm.), Portunus, Cambarus propinquus (10.6 
to 19.0 mm.), Cambarus bartoni and Palemon. In one case 
there is no evident change with age (Palamonetes) and in a few 
there is a decrease with age (Ophioglypha above 15 mm., Ambly- 
stoma and Cambarus propinquus young as compared with adults). 
The specific rate of regeneration or the rate per unit of length 
of the individual is however usually less in older than in younger 
individuals, so that it takes them longer to complete a removed 
appendage than in the younger ones. Examples are: Cassiopea, 
Ophioglypha, (above 15 mm.), Amblystoma, C. bartoni, C. pro- 
pinquus, Palzmon, Palemonetes (in part). In a fewcases there 
is no change in specific rate with age (Ophioglypha, medium 
individuals, Portunus (!),‘ Palamonetes, in part), or there is 
an increase with age (Ophioglypha, smaller individuals,® Por- 
tunus ( ')?°). 
DISCUSSION 
The experiments as a whole confirm the general conclusion 
that in older individuals it takes longer to complete a removed 
organ than in younger ones.7 This general result is usually 
evident in extremes of age without the use of any accurate measure- 
ments. As has been previously pointed out there are however 
undoubted exceptions to the rule, the most marked in the present 
set of experiments being the chele of Portunus and probably the 
younger individuals of Ophioglypha. 
The accurate measurements of regenerating appendages has 
brought out the point upon which special emphasis needs to be 
laid, and this is the fact that in a majority of the species studied 
the actual rate at which new tissue is proliferated is greater in 
the older individuals than in the younger ones. The older indi- 
viduals when they lose an appendage obviously have more mate- 
rial removed than do the younger ones, but the proportion of 
removed material to the whole mass of the body is not materially 
changed in those forms in which growth does not involve a change 
4 See special condition affecting the size of the chele, p. 568 of this paper. 
18 Data not conclusive. 
6 See special conditions affecting the size of the chele, p. 568 of this paper. 
17A full bibliography is given in Przibram. Experimental-Zodlogie. II. Regeneration. 1909. 
