CIRRIPEDIA 



383 



antennules. The whole trunk, with its muscles and appendages, is 

 now thrown off and a new cuticle formed under the old one, with a 

 dart-like organ which is thrust through the antennule and the thin 

 cuticle at the base of the seta of the crab into the body of the latter. 

 Through the dart the remnant of the larva, a mass of undifferentiated 

 cells surrounded by a layer of ectoderm, passes into the host's body 

 cavity. Carried by the blood it becomes attached to the under side 

 of the intestine (Fig. 259). There rootlets begin to grow out from it 

 and eventually permeate the body of the crab to the extremities of the 



Fig. 258. Larval stages of Sacculina. From G. Smith. A, Nauplius, B, 

 Cypris. A.i, antennule; A. 2, antenna; Ab. abdomen; E. undifferentiated 

 cells; F. frontal horn with gland cells; GL gland cells; Md. mandible; Ten. 

 frontal tentacles (frontal organs) ; Tn. tendon. 



limbs. Meanwhile a knob also grows from the mass; forms within 

 itself a mantle cavity surrounding an internal "visceral mass" which 

 contains the rudiments of genital organs and a ganglion ; presses upon 

 the ventral integument of the abdomen of the host, whose cuticle 

 is thus hindered from forming at that spot ; and consequently at the 

 next moult of the crab comes to project freely under the abdomen, 

 where it may be found in the adult condition. 



The phenomenon known as parasitic castration is exhibited by 

 crabs attacked by Sacculina. The moult at which the parasite becomes 

 external produces a change in the secondary sexual characters in the 



