Fiir Darwin. 



-'63 



growth, and of producing a numerous progeny. With the further development, 

 assisted by natural selection, of the roots embracing the intestine of the host and 

 spreading amongst its hepatic tubes, the introduction of nourishment through the 

 mouth and all the parts implicated in it, such as the whirling cirri, the buccal 

 organs, and the intestine, gradually lost their importance, became aborted by 

 disuse, and finally disappeared without leaving a trace of their existence. Protected 

 by the abdomen of the Crab, or by the shell inhabited by the Pagunts, the 

 parasite also no longer required the calcareous test, in which, no doubt, the first 

 Cirripedes settling upon these Decapods rejoiced. This protective covering, having 

 become superfluous, also disappeared, and there remained at last only a soft sack 

 filled with eggs, without limbs, without mouth or alimentary canal, and nourished, 

 like a plant, by means of roots, which it pushed into the body of its host. The 

 Cirripede had become a Rhizocephalon. 



If it be desired to form a notion of what our parasite may have looked like 

 when half way in its progress from the one form to the other, we may consult 

 the figures given by Darwin (Lepadidse PI. IV., figs, i 7) of Anelasma squalicola. 

 This Lepadide, which lives upon Sharks in the North Sea, seems, in fact, to be in 

 the best way to lose its cirri and buccal organs in the same manner. The widely- 

 cleft, shell-less test is supported upon a thick peduncle, which is immersed in the 

 skin of the Shark. The surface of the peduncle is beset with much-ramified, 

 hollow filaments, wich "penetrate the Shark's flesh like roots" (Darwin). Darwin 

 looked in vain for cement-glands and cement. It seems to me hardly doubtful, 

 that the ramified hollow filaments are themselves nothing but the cements-ducts 

 converted into nutritive roots, and that it is just in consequence of the development 

 of this new source of nourishment, that the cirri and buccal organs are in the 

 highest degree aborted. All the parts of the mouth are extremely minute; the 

 palpi and exterior maxillse have almost disappeared; the cirri are thick, inarti- 

 culate, and destitute of bristles; and the muscles both of the mouth and cirri are 

 without transverse striation. Darwin found the stomach perfectly empty in the 

 animal examined by him. 



