220 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
The results show clearly that within very broad limits it is impossible to tell the 
age of a star fish from its size. Star-fishes of all ages are able to live for months with 
very little or no food. The rate of growth depends directly upon the amount of food 
eaten. Star-fishes which are regenerating one, or even two, arms may, under ordinary 
circumstances, grow as rapidly as the complete stars. The growth of the new arms 
in the star fish experimented upon was slightly more rapid than that of the original 
arms, showing a tendency in the organism to return to the original length In four 
months from time of setting, some of the larger stars kept in the cars under favorable 
circumstances attained a length of from 50 to 54 mm., or 2 to 2J inches, measured 
from mouth to tip of arm. This is more than twice the length of many of the stars 
which were found just before the beginning of the breeding season, and which were 
therefore at least nearly a year old. 
Allowing a moderate amount of growth during the winter and spring months, of 
10 to 15 mm. (the amount of increase attained in one full month preceding October 12), 
the larger year-ohl star-fish in the early summer would be about 65 mm., or 24 inches, 
in length, which is about the length of the greater number of stars taken on the mops 
in the Kickemuit River during the summer. 
XI. Wliat is the size and age at, sexual maturity? 
Among the star fish caught in various parts of the bay on June 2, 3, and 4, several 
specimens only l^- inches, or 32 mm., were found to be very full of sexual products. 
This size was attained by many of the star-fish reared in tbe car on September 26, 
about three months from the time of setting. See table on page 217. # Great numbers 
of stars measuring about 2 inches, or 50 mm., were found ripe the first week of June. 
This was the size of several specimens in the car on October 25, which were not more 
than four months old, and whose sexual glands were well developed. In other words, 
a large number of the star-fish reared in the car were by the end of October as large as 
a great many which were sexually mature in June. Moreover, it was rare to find a 
specimen of this size on the 1st of June which was not full of ripe eggs, which were 
laid later, as the empty star-fish caught in July showed. It is an obvious conclusion, 
therefore, that, with fairly good opportunities to obtain food, the star-fish becomes 
sexually mature in less than a year, and that those hatched one season breed the next. 
In his monograph on Xorth American star fishes, Alexander Agassiz gives his 
views with reference to their rate of growth in the following words (the figures 
referred to represent specimens, all of them smaller than that in our fig. 9, of a star 
about 2 weeks old raised in the car) : 
The young star-fishes figured on this plate (pi. vin) were all found attached to roots of Laminaria, 
thrown up on the beaches, in the neighborhood, after a storm; and from their different stages of 
growth, as compared with the oldest star-fish raised from a Brachiolaria (pi. vi, fig. 11), specimens of 
which -were also found upon these roots, it is probable that the sizes here figured are 1 (fig. 1), 2 
(iig. 8), and 3 (fig. 10) years old. A considerable number of specimens were picked up in this way, 
and they could all be arranged into very distinct groups, representing the star-fishes of the present 
and of two previous seasons. There seemed to he no gradation from one group to another, such 
as we have among the young sea-urchins, which, in consequence of their manner of breeding during 
the whole year, form series the relations of which it is impossible to determine. In this connection 
I would say that by arranging the star-fishes found upon our rocks into series according to their 
size we are able to obtain a rough estimate of the number of years required by them to attain their 
full development; this I presume to be somewhere about fourteen years. t They begin to spawn 
v Eggs from a specimen of 38 mm. were readily fertilized with spermatozoa from amale of same size. 
tFor an account of the method adopted by Professor Agassiz for ascertaining the age of many 
of our marine animals, see Proceed. Essex Inst., 1863, p. 252. 
