1909.] THE SHELL-GROWTH OF THE LIMPED PATELLA VULGATA. 235 
EXPLANATION OF ABBREVIATIONS IN TEXT-FIGURES. 
Abd.c. Abdominal cavity. | P.hp.spt. Post-hepatic septum. 
A.int.as. Anterior intermediate air-sac. | Ph.rs. Pulmo-hepatic recess. 
Cf. Line of fusion of celomic epi- | P.int.as. Posterior intermediate air-sac. 
thelium of post-pulmonary | Pl.c. Pleural cavity. 
Septum with that of lateral | PJ.hp.c. Pulmo-hepatic cavity. 
body-wall. | Plt. Pulmonary rudiment. 
Ct.pl.m. Costo-pulmonary muscles. P.pl.spt. Post-pulmonary septum. 
D.ms. Median dorsal mesentery. P.p.p.m. Pericardio-pleuro-peritoneal 
D.pl.lg. Dorsal pulmonary ligament. membrane. 
z. Gizzard, Pin. fd. Pronephric fold. 
Ht. Heart. | Pt.c. Peritoneal cavity. 
Kd. Kidney. | Spl. Spleen. 
Ing. Lung. |  WSp.rnl. Supra-renal body. 
Lv. Liver. | S¢. Stomach. 
Mi.dé. Miillerian duet. Um. Umbilical opening. 
Ob.1g.lv. Oblique ligament of the liver. | V.lv.s. Ventral liver-sac. 
(Hs, (Esophagus. Pms. Median ventral mesentery. 
P.as. Posterior air-sac. | V.pl.lg. Ventral pulmonary ligament. 
Pe. Pericardium. | Wy.by. Wolttian body. 
P.hp.c. Post-hepatic cavity. 
2. The Growth of the Shell of Patella vulgata L. 
Biv 1d, SS). Levorsetaore, Wilk 
[Received February 16, 1909. ] 
(Plate XXXII. +) 
This paper consists of two parts; the firsta study of the rate of 
growth of the lmpet-shell, the second a study of the gradual 
change in the shape of the shell as it grows in size. Throughout the 
paper the size of the shell has been taken as a measure of its growth. 
Owing to the manner in which growth takes place, no dimension 
of the shell can increase without a corresponding increase in 
the other dimensions, so that any one dimension may be taken 
as a measure of growth, 7. e. of increase in size. It is convenient 
to take length as a measure of size. Knowing the length one can 
calculate with a fair degree of accuracy all the other dimensions, 
if one has previously determined the average ratios of the other 
dimensions to length for successive values of the length. 
I. Rare or Grows. 
1. Breeding Season. 
The fact that limpets of 5 mm. in length may be found in 
January and in July leads one to suppose that the breeding 
season is of considerable duration, and the observations which I 
have made fully confirm this opinion. 
I tried to discover at what time of year small limpets chiefly 
appear, by watching events in the small bay where I studied the 
growth of the limpet. On January 11th, 1908, there was a 
** Communicated by Prof. J. ARTHUR THomson, F.Z.S. 
+ For explanation of the Plate see p. 253. 
16* 
