1909.] OF THE LIMPET PATELLA VULGATA. 249 
TABLE VII. 
Mean Ratios. 
| L Ab L H 
Group. No. ! B At: ‘ar B 
| 5—10 mm. Ne 1:32 1:64 3°52 375 
, OS 109 129 | 1:57 3°66 ta 352 
| 150) 163 1:27 1:46 2:95 “431 
| 20-25 . | 91 1:25 1:44 3°33 ‘375 
(DRS) So VGH 1:23 1:36 Ss genes os 
2035 68 121 1:34 PRey( ally 2, ED 
35—40 ,, 81 119 131 265 | 449 
| 4045. 115 ii 1:26 DS al ml 
\ ZIG 0) 9 138 116 1:24 2°28 509 
| 5055 ,, 122 115 1:22 2°16 532 
| 55—60 ,, 25 115 77 2:28 504 
As is eT in Table VII. very considerable changes take 
place in the shape of the limpet-shell during its growth from 
5 mm. to 60 mm. long. 
L 5 E F 
po Lhe shell becomes gradually broader in proportion to its 
length, and this change is remarkably uniform from group to 
group. 
W pol’ grows higher in proportion to its length and in 
proportion to its breadth. This change is on the whole a con- 
tinuous one, but a reversal of its direction in both cases takes 
place in the transition from the first to the second, from the 
third to the fourth, and from the second last to the last groups. 
Ab 
IG 
anterior margin (Af) becomes greater with great uniformity in 
proportion oy the distance between the apex and the posterior 
margin (Ab). It does not follow that the apex shifts backwards. 
The changes in the position of the apex may be represented graphic- 
i 5 : hi FF iN 
ally if the successive values of the ratios Ht and a are drawn 
to scale on a constant L. It appears from such figures that the 
apex of the shell shifts gradually backwards during growth from 
5 mm. to 25 mm., and then remains practically stationary till a 
leneth of 55 mm. is reached, when it again shifts backwards. 
Most of these changes can be directly inferred from the shape 
of a typical fully-grown limpet-shell. A small limpet-shell has 
the shape of a flattened excentrié cone, and the apex is in 
such a young shell finely pointed and turned forwards. As 
growth proceeds the sides of the cone do not grow straight 
on, but begin to curve inwards slightly, so that by the time the 
shell reaches a length of 50 mm. its outline as seen from the side 
may be such as is shown in the Plate (last row). All good-sized 
limpet- shells show this ‘ingrowth ” in the anterior and posterior 
regions of the shell, and alge at the sides of the shell, for a similar 
ee ingrowth ” takes place there also. This general “ingrowth ” 
Proc. Zoou. Soc.—1909, No. XVII. eouial 77 
—The distance in a straight line between the apex and the 
