Ill 



OF THE GROWTH OF SHELLFISH 



167 



the actual rate remains unknown. It grows a little longer and 

 narrower with age. Its weight-length coefficient (of which we shall 

 have more to say presently) increases as time goes on, and appears 

 to follow a wavy course which might be accounted for if the 

 shell grew thinner and then thicker again, as if ever so little more 

 lime were secreted at one season than another. The growth of a 

 shell, or the deposition of its calcium carbonate, is much influenced 

 by temperature; clams and oysters enlarge their shells only so long 

 as the temperature stands above a certain specific minimum, and 

 the mean size of the same hmpet is very different in Essex and in 

 the United States*. Curious peculiarities of growth have been 

 discovered in slipper-hmpets. Young limpets clustered roimd an 

 old female grow slower than others which Uve sohtary and apart. 

 The solitary forms become in turn male, hermaphrodite and at last 

 female, but the gregarious or clustered forms . develop into males, 

 and so remain; development of male characters and duration of 

 the male phase depend on the presence or absence of a female in 

 the near neighbourhood. 



Measurements of slipper-limpets 

 {From J. H. Eraser's data, epitomised) 



Mean 1-87 



89-3 



* Cf. J. H. Fraser, On the size of Urosalpinx etc., Proc. Malacol. Soc. xix, 

 pp. 243-254, 1931. Much else is known about the growth of various limpets, 

 their seasonal periodicities, the change of shape in certain species, and other 

 matters; cf. E. S. Russell, Growth of Patella, P.Z.S. cxcix, pp. 235-253; J. H. 

 Orton, Journ. Mar. BioL Assoc, xv, pp. 277-288, 1929; Noboru Abe, Sci. Rep. 

 Tohoku Imp. Univ. Biol, vi, pp. 347-363, 1932, and Okuso Hamai, ibid, xii, 

 pp. 71-95, 1937. 



