THE AMERICAN NATURALIST 



[Vol.L 



the spine bearing the conchodermas became detached in the 

 course of the animal's self-inflation. It is probable, therefore, 

 that the spine would soon have been shed under natural circum- 

 stances. 



Several features of the behavior of these conchodermas are of 

 interest in comparison with those of other barnacles. Some years 

 ago it was reported by Pouchet et Joubert (1876) that cirripedia 

 'attached to rocks reacted to shading, while those attached to 

 floating objects did not ; their inference being that to the station- 

 ary barnacles a shadow signified danger, whereas, to those borne 

 about at the surface of the water, a fluctuating illumination was 

 the normal state of affairs. This observation has been regarded 

 as an instance of adaptation comparable with that of Hargitt 

 (1909) on the gradual loss of reaction to shading when serpulids 

 are maintained in the laboratory. 



The specimens of Conchodfrnui attached to Diodon did not re- 

 act to shadows under any of a number of experimental condi- 

 tions. They seem, therefore, to be in agreement with the obser- 

 vation of Pouchet et Joubert. But tests upon lepads found upon 

 floating timbers and upon Ascophyllum showed that Lepas 

 anserifera and L. pectinata do respond to shading by retracting 

 the legs and approximating the valves. From a number of tests 

 it appeared that neither the legs nor valves are sensitive to shad- 

 ing, but that the shadow must affect some part of the body within 

 the shell suggesting that the persisting nauplius eye is the 

 organ involved. The extent of the response varies with the de- 

 gree to which the appendages have been extruded: when just 

 being extruded, they re'act by complete retraction; when fully 

 extruded, by a partial retraction ; after being fully extruded for 

 one or two minutes, they react to shading quite promptly and 

 completely. After completion of a response there must usually 

 elapse from two to four minutes before another reaction can be 

 secured. 



It seems to me, then, that the supposed adaptation of floating 

 barnacles is not of the nature which has been supposed. Whether 

 the non-reaction of Conchoderma to shading is properly to be 

 considered a direct adaptation is therefore questionable. The 

 host of these particular specimens is not a surface fish, and the 

 absence of sensitivity to shading may be due to their deep 

 habitat, Direct sunlight inhibited the rhythmic movements of 

 the conchodermas, and they were much more active at night than 

 in diffuse laboratory light. 



