246 



BULLETIN OP THE BUREAU OF FISHERIES 



It is evident, therefore, that light rays in the field of blue-green have a much 

 greater effect in activating the cyprid larvse of barnacles than the light rays in other 

 fields of the visible spectrum. 



REACTIONS OF LARVAL BARNACLES TO LIGHT AT TIME OP ATTACHMENT 



It has been demonstrated that the larval barnacles are sensitive to light and 

 respond more vigorously to light in the blue-green portion of the spectrum than to 

 light of other color. That these organisms are negative to light at the time of attach- 

 ment was demonstrated by isolating a number of the cyprids and placing them in 

 small cubical aquaria, which were then covered with black paper on five of their 

 six sides. The uncovered side was exposed to light from a north window. 



The results of these experiments, which were repeated on several occasions, can 

 be seen in Figure 39. It will be noted that in each dish the cyprids attached in that 



half of the contaiuer away from the source of 

 light, and that in each case the individuals were 

 so oriented as to be directed away from the 

 source of illumination. 



It can be seen clearly from these experiments 

 that for the two types of barnacles that were 

 tested, light is an important factor in determin- 

 iug the point of attachment, and that they 

 orient themselves with their anterior ends 

 directed away from the source of light. 



It would appear evident from the results of 

 the submerged colored panels, from the sub- 

 merged tiles, from the experimental data on 

 reaction of cyprid larvse to spectral color, and, 

 finally, from the above experiment, in which it 

 is shown that cyprid larvse become negative to 

 light at the time of attachment, that paints 

 varying from a light blue to yellow would 

 accumulate the least amount of fouling, and 

 that a light green paint probably would be the most efiicient, all other factors 

 being equal. 



Process of attachment of the larvse of barnacles. — After a free-swimming period of 

 from three days to several weeks, the cyprids attach to some substratum and meta- 

 morphose into the adult type of barnacle. When the internal physiological con- 

 ditions necessary for attachment are present, apparently correlated with the "lipoid" 

 content of the organism, the larvse have been observed, on many occasions, to 

 "walk" on the substratum, apparently hunting a place for attachment. This re- 

 markable performance is accomplished by alternate attachment and release of the 

 adhesive tips of the antennse, combined with the relaxation and contraction of the 

 set of appendages, which result in giving the organism a forward movement. (Fig. 

 40.) In this manner these organisms have been observed to "walk" for considerable 

 distances, and have been seen to "test" various areas for a period of more than an 

 hour before finally attaching, 



Fig. 40. — Successive movements of a cyprid barnacle 

 larva at the time of "selecting" a place of attach- 

 ment 



