PLEOTROPISM 41 



simply pelagic, rather than as negatively stereo- 

 tropic. On the contrary, it is the intrinsic and 

 latent stereotropism of the larvse which leads 

 to the statozoic habit of the adult. 



Furthermore the nauplii of Cirripedes are well 

 known to be markedly heliotropic, 1 and this 

 character might temporarily mask their potential 

 stereotropism, leading them out into the open 

 sea. Groom obtained them in large numbers 

 in the tow-net at Plymouth during February 

 and March, 1893, belonging to a species which 

 lives on the limestone rocks below the labora- 

 tory, in places considerably above high-tide 

 mark, where they can only be moistened by 

 the passing foam ; but he was unable to rear 

 them in confinement. 



The Gastropod mollusca (snails, slugs, lim- 

 pets), with their creeping adhesive foot, are 

 pre-eminently stereotropic ; yet it is not doubted 

 that the typically pelagic or pleotropic Hetero- 

 poda and Pteropoda have been derived from 

 them along different lines of descent. The 

 free-swimming veliger larva of mollusca might 

 be described equally well with the nauplius of 

 Balanus, as showing negative stereotropism, and 

 as indicating a free-swimming ancestry. It 

 seems more just to suppose however that larvae 



1 i. T. T. Groom. " On the Early Development of Cirripedes." 

 Phil. Trans., London, vol. clxxxv., 1894, pp. 1 19-232. 2. A. Gruvel, 

 " Monographic des Cirrhipedes," Paris, 1905, p. 445. 



