322 J. H. ORTON. 



specimen grew from a length of 25 mms. and a width of 17 mms. to a 

 length of 29 mms. and a width of 20-5 mms. ; the other one grew from a 

 length of 28 mms. and a width of 13 mms. to a length of 33-5 mms. and 

 a width of 26 mms. It is thus seen that C. fornicata may grow to a length 

 of at least 3 cms. within 2| years, but it is desirable that the rate of 

 growth should be observed in a larger number of individuals than was 

 possible under the conditions of these experiments. 



THE AGE OF SEX-CHANGE IN CREPIDULA FORNICATA. 



In the tray experiment just described it was found that some of the 

 small Crepidula had formed chains of two individuals, and in one case 

 two specimens had put themselves in chain with one of the larger marked 

 Crepidula to form a chain of three. When measuring these slipper- 

 limpets their sex condition was also recorded and the singular fact 

 established that while the individuals in chain were quite vigorous males, 

 those which were leading a solitary life were changing from males into 

 females. This phenomenon had indeed been suspected from the exten- 

 sive examinations which have been made from time to time during the 

 last few years on batches of Crepidula. The condition of these small 

 Crepidulas may be gathered from the following records in which the 

 abbreviations used in an earlier paper* are again adopted. The solitary 

 specimens were recorded as follows : 8 specimens (^ p.sm. ; 3 (^ p.tr. ; one 

 p.r.ut.r. ; 2 $ ut.sm.p.tr. ; 4 or 5 3^. In the chains formed by the small 

 specimens (one year old forms) the sexes were recorded as follows : (1) 

 A $ p.r., B ^ ; (2) A ? ut.r.? p.r., B ^. The chains formed by the small 

 specimens with the larger marked specimens, which in all cases are the 

 A's in the chain, were recorded as follows : A I sex not recorded, B (J, 

 C (J ; A II $ p.tr., B (^ ; A IV ? p.tr., B ^. Thus in all cases where the 

 young Crepidula had formed chains they retained their characters as 

 males, whilst 14 out of 19 that remained solitary had begun to change 

 their sex. Thus the absence of association with their fellows in chains 

 undoubtedly results in a more rapid change from the male condition to 

 the female condition than m the cases where the Crepidulas are able to 

 form chains. Sex-change in Crepidula therefore may take place in the 

 second year of the life of isolated individuals. 



* J. H. Orton, " On the Occurrence of Protandric Hermaphroditism in Crepidula 

 fornicata;' Proc. Roij. Soc. B., Vol. 81, 1909. 



The meaning of the abbreviations used above is as follows : — 

 p.sm. = penis small ; p.tr. = trace of penis ; p.r. = penis rudimentary. 

 ut.sm. = uterus small ; ut.r. = uterus rudimentary. 



