44 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



is shed. The maturation of the sperm and the eggs and the fertiliza- 

 tion of the latter are fully described by Smith, but here ends our 

 discussion of the metamorphosis of Sacculina. 



Fig. 17. — Cirripedia ; Rhizocepliala. Internal and external parasitic stages. (A-D 

 from G. Smith, 1906; E, F from Potts, 1915.) 



A, Sacculina neglecta attached on intestine of crab Inachus scorpio. B, same, 

 later stage with root system developed. C, PeUogaster sp., diagrammatic cross 

 sction of parasite after emergence on ventral side of crab. D, same, longitudinal 

 section. E, Thompsonia sp., part of root system in tail fan of crab Synalpheus 

 brucei, with external brood sacs. F, same, external sacs on chela of Thalamita 

 prymna. 



a, internal reproductive buds ; b, external brood sac containing cypris larvae ; 

 be, brood cavity; c, external sac with all but a few larvae escaped through 

 terminal aperture {op) ; Gng, ganglion; mn, mantle; Od, oviduct; op, external 

 opening of brood cavity; Ov, ovary; r, nutritive roots; Tcs, testis. 



The parasitization of the crab by Sacculina adversely affects the 

 gonads and results in structural changes of the host called parasitic 

 castration. At the moult accompanying the emergence of the parasite, 

 the male crab takes on certain female characters and the female suffers 



