RHIZOCEPHALA. 



225 



seta to which the Cyj^^'^s-like larva attached itself. Through this 

 membrane the arrow bores, thus establishing a communication between 

 the inner cavity of the sac and the body-cavity of the host. During 

 these processes the soft inner body becomes surrounded with another 

 very delicate cuticle (third moult of the Kentrogon stage). 



There is at this point a gap in our knowledge of the development 

 of Saccnlina. There can, however, be no doubt that the soft body 



Fig. 109.— Longitudinal sections through two stages of development ot Saccnlina carcini (after 

 Delage). .-1, Saccnlina interna. B, Saccnlina externa, a, atrium (widening of the oviduct); 

 a»)i, outer mantle-layer ; &, brood-ca\'ity (mantle-cavity) ; B, basal membrane ; C, central 

 tumour ; cl, cloacal opening ; D, intestinal wall of the host ; dr, glands of the ovarian sac ; 

 /, aperture of the perivisceral cavity ; g, ganglion ; im, inner mantle-layer ; L, body- wall of 

 the host ; ov, ovary ; p, perivisceral cavity ; pe, perivisceral ectodermal layer ; R, root- 

 processes (some in cross section) ; t, rudiment of testes. 



of the larva passes through the canal of the arrow, so as, in this way, 

 to reach the body-cavity of the host. The Sacculina thus becomes 

 an endoparasite {^Sacculina interna). 



Q 



