Chap. XII. EVOLUTION OF THE EHIZOCEPHALA. 139 



appeared without leaving a trace of tlieir existence. 

 Protected by the abdomen of the Crab, or by the shell 

 inhabited by the Pagurus, 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 Khizocephalon. 



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, (Lepadidae PI., iv., figs. 1-7) 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, which " 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 cement-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 



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