218 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
The following experiments on the rate of growth support this view: 
(c) Rate of growth of individual star-fishes Icept under various conditions. — The 
largest of the stars in the car on August 18 (compare fig. 15) was kept in a dish with 
only a few very small barnacles for food. When taken from the car, it measured 18 
mm.; slightly more when fully expanded. On September 25 it measured 18 mm., 
showing no growth. On September 20, 39 days after it was taken from the car, it 
measured between 15 and 16 mm. In the absence of food, therefore, it had lived and 
apparently was in perfect health, but had probably diminished somewhat in length, 
as well as in bulk. (Some allowance must, of course, be made for the contraction and 
expansion, as mentioned before.) During this time several of the stars, smaller than 
this one, remained in the car and grew to the length of 35 mm. (Fig. 17.) 
A small star-fish which was caught in the tow, and which set on June 28, was 
kept in the dish with many others until June 23. On this date it was placed in a small 
dish by itself and fed with small clams and barnacles. Fig. 23 shows the growth of 
this specimen : a, 2 mm., July 23; 5, 4 mm., August 13; c, 41 mm., August 18; d, 5 mm., 
September 0. On September 6 it was transferred to a car where there was an abund- 
ance of small barnacles. Fig. 23, e (12 mm.), represents size on September 26 ; /, 21 mm., 
on October 12; g , 30 mm., on November 5. 
As a control of this experiment, several star-fish, which also set on June 28, were 
kept with a minimum amount of food. One of these, photographed at natural size on 
September 6, is shown in fig. 2L a, while the largest star in the car (with plenty of 
food) is represented in fig. 21 h (27 nun.). The specimen figured in a is 39 days old, 
and that in h is within a day or two of that age. 
The next experiment (illustrated by fig. 22) on the growth of stars was as follows: 
On August 3 two stars of average size were taken from the original car and placed 
in another car with a bunch of mussels. 
On August 3 (No. 1) = 7 mm., fig. a. On August 16 (No. 2) = 101 mm., fig. a'. 
During this time the stars had little or no food, since they could not, or would 
not, eat the mussels. On August 15 a lot of barnacles was placed in this car, and by 
September 5 the results of the new food were evident enough: 
September 5: (No. 1) = 15 mm., fig. c (one arm was torn off in measuring). (No. 
2) = 19 mm., fig. c'. 
September 26: (No. 1) = 28 mm., fig. d (new arm 10 mm. measured from mouth, 
growth of 7 mm.). (No. 2) = 29 mm., fig. d'. 
October 12: (No. 1) = 36 min., fig. e (regenerating arm, 20 mm., from mouth, 
growth of 17 mm.). (No. 2) = 41 mm., fig. e'. 
From August 3 to August 16, while these specimens were not growing at all, 
those in the car grew about 6 mm. These two specimens afterwards, however, having 
more food and no interference in eating it, made up this difference, and by September 
26 had grown as much as those in the original car. 
One interesting point brought out by the experiment is that a star which is 
regenerating an arm may grow as fast as a complete star. Compare next experiment. 
(d) Rate of growth and rate of regeneration. — The star-fish,like the lobster and many 
crabs, has the habit of dropping off an arm which has been mutilated and regenerating 
a new one. Unless the arm is mutilated or some other shock administered, one may 
sometimes tear a star in two by pulling on the arms, while the latter still remain on 
the fragments of the disk. On the other hand, if the suckers are cut off from one arm, 
or the arm is crushed or cut several times, it will usually drop off, always at the same 
point near the disk, taking the sexual glands with it. 
