ARTHROPODA 



'57 



shell the feathery appendages may be protruded; of thi 

 there are six pairs, attached to the thorax The body itself 

 does not appear segmented, and terminates posteriorly in an 

 elongated copulatory organ, or penis. Since these barnacles 

 occur so frequently on wood, the belief arose some centuries 

 that they were of vegetable origin, while the feathery, thoracic 

 appendages suggested an association with birds, so that many 

 of the earlier writers on natural history maintained with convic- 



Fir.. 149. Lepas anatifera, the goose-neck barnacle. A. external view; B, internal struc- 

 ture, a' , antennule ; c, carina ; cd, cement gland ; /, digestive gland ; m, adductor muscle; 

 od, oviduct; ov, ovary; /> (in A) peduncle and (in H) penis; s, scutum ; t, tergum and 

 testis; vd, vas deferens. (Alter Darwin and Claus, from Parker and Haswell's Manual.) 



tion that geese developed directly from barnacles ; one writer 

 asserts that he has seen the process. 



The stalkless barnacles have very much the same structure 

 as the goose-neck, but they are provided with a much firmer 

 shell (Fig. 150), the body being surrounded by a sort of wall. 

 often very thick and with sharp edges, and consisting of immov- 

 able plates. There are movable plates covering the free or 

 ventral surface of the animal, between which the appendages 



