348 



PHYLUM ARTHROPODA 



yolk and the carapace, are lost ; a little sac remains, which passes into 

 the interior of the crab. It reaches the abdomen, and, as it approaches 

 maturity, the integuments of the crab are dissolved beneath it, and 



Fig. 192. — Sacculina as a parasite on a female crab. — After Delage. 



The abdomen of the crab has been drawn back, showing the bean-shaped 

 Sacculina. A., Anus of crab ; R., reproductive aperture of the parasite. 

 The dark-coloured branches are the absorbent root-like processes of 

 Sacculina, supposed to be visible through the crab's shell. They 

 extend even into the limbs. They are shown on one side only. 



the sac-like body protrudes. It appears to live for three years, during 

 which time the growth of its host is arrested, and no moult occurs. 

 In some cases the parasitised male crab puts on feminine characters, 

 and the testis is replaced by egg-producing tissue. In a parasitised 



