1909. | OF THE LIMPET PATELLA VULGATA. DAT 
40 mm. on July 14th, and 45 mm. on Nov. 23rd. But actually the 
second year-group attains to a length of only 38 mm. even by 
December 31st. 
5. Rate of Growth and Reproduction. 
We have seen that the variations in the rate of growth of the 
limpet’s shell depend upon the age of the shell and upon the 
temperature. It is natural to enquire whether the attainment 
of sexual maturity has any marked effect wpon the rate of growth. 
In other words, does arrival at a state of maturity coincide 
with any marked drop in the rate of growth? It would seem 
that it does, for sexual maturity is attained between 20 mm. and 
25 mm., and there is a marked fall of the rate of growth at 
25 mm. to half what it was at about 20 mm. Growth, however, 
continues for long after a length of 25 mm. is reached, and ceases 
only at 50-60 mm. The average full-grown size is about 45- 
50 mm. The limpet shell therefore doubles its length after 
sexual maturity has been reached. This fact recalls the law of 
growth which Dr. Fulton has formulated for fish, that they 
‘approximately double their size and increase their weight about 
eight times after they have reached sexual maturity.” (4. p. 182.) 
After the attainment of sexual maturity the shell becomes 
much thicker and more solid in build. This increase in thickness 
is no doubt correlated with its slower growth. 
6. History of the Growing Limpet. 
The facts detailed above enable us to form a mental picture of 
the life-history of the limpet once it has settled down upon the 
shore as a miniature adult. 
It may come into existence at any time from July to January. 
Its larval existence lasts probably only a week or two and it 
settles down as a minute shell, one or two mm. in length. 
Growth is rapid during the autumn. By January the shell is on 
the average about 10 mm. long, and during January and February 
it grows say 2mm. The rate of growth is then accelerated, and 
growth continues actively throughout the summer. In August or 
September the limpet, which is now 20-25 mm. in length, becomes 
sexually mature. The rate of growth, which has hitherto been 
anything from 12—20 per cent. per month, now falls abruptly on 
the approach of winter and after the ripening of the gonad. By 
the month of December the limpet is on the average 29 mm. 
long. Very little increase of size is manifested during the early 
months of the second year, but by April a slow growth sets in at 
the rate of 5-7 per cent. per month, which falls off after the 
summer is past to 1-2 per cent. and finally in the early winter 
months ceases almost completely. During this year the gonad 
has undergone profound changes, returning in the early spring to 
a state almost of primary indifference and gradually ripening as 
the summer advances. The gonad attains its full size in this 
