98 



CRUSTACEA CIRRIPEDIA 



CHAP. 



of the crab's intestine, at the 

 abdomen, all the adult organs are 

 the whole structure is surrounded 

 by invagination known as the 

 The young " Scwculina interna " 

 some time, and being applied to 

 of the crab just at the point wheri 



unction between thorax and 

 laid down in miniature, and 

 by an additional sac formed 

 perivisceral space (Fig. 70). 

 remains in this position for 

 the ventral abdominal tissues 

 e thorax and abdomen join, or 



Fig. 69. — The raid-gut of Inachus 

 OYUxwitanicits with a young Saccu- 

 ^ma overlying it, X 2. c.^, "Cen- 

 tral tumour" of the parasite; 

 d.i, d.s, inferior and superior 

 diverticula of alimentary canal 

 of host ; n, "nucleus," or body- 

 rudiment of Saccidino- ; r, its 

 roots ; X, definitive position of 

 the parasite. 



Fig. 70. — Later stage in the develop- 

 ment of the "SricruHna interna," 

 X 2. b. Body of Saccnlina ; c.t, 

 "central tumour"; d.i, d.s, in- 

 ferior and superior diverticula of 

 alimentary canal of host ; o, open- 

 ing of perivisceral cavity of Saccu- 

 liiia ; T, its roots. 



a little below it, it causes the crab's epithelium to degenerate, so 

 that when the crab moults, a little hole i.s left in this region of 

 the same size as the body of the SaecuUna, owing to the failure 

 of the epithelium to form chitin here ; and thus the little 

 parasite is pushed through this hole and comes to the exterior 

 as the adolescent " Sacculina externa." From this point onwards 

 the crab, being inhibited in its growth through the action of the 

 parasite, never moults again ; so that the Sacculina occupies a 

 safe position protruding from the crab's abdomen, which laps over 



