STEREOTROPISM 39 



this case a function of the stereotropism of the 

 spermatozoa." [Loeb., loc. cit.~\. 



As an instance of the negative working of 

 the same reaction, Loeb quotes the case of the 

 nauplii of Balanus. This does not appear to 

 be so successful ; it means either very little, or 

 something which I do not understand. Referring 

 to positive stereotropism, which I regard as a 

 factor of great potentiality, Loeb explains that it 

 is no real tropism inasmuch as lines of force do 

 not exist. Much less then must negative stereo- 

 tropism be responsive to force of any descrip- 

 tion ; not only is it a negative quality, it is, as 

 we shall see, practically nothing beyond words. 



The acorn barnacles (Balanidae) make up the 

 familiar crowded communities of white shelly 

 bodies which are firmly attached to rocks 

 between tide marks, and to other suitable sur- 

 faces. All barnacles are fixed, but these are 

 doubly statozoic, cemented by their flat base 

 without a stalk, in contrast with the goose 

 barnacles (Lepadidae, pedunculate Cirripedes) 

 which hang by a stalk attached to logs and 

 other floating objects, sometimes to fishes, sea 

 snakes, sea birds, and Crustacea. 



The stalked barnacles, although fixed, chiefly 

 affect what may be termed a planozoic (vagrant) 

 habit analogous, up to a certain point, with 

 that of ectoparasites. Commonly associated 

 with floating communities of Lepas, are two 



