CIRRIPEDIA 385 



limbs give off sacs which become external at a moult of the host. 

 These sacs contain neither ganglion, generative ducts, nor testes, but 

 only a number of ova in a space of doubtful nature. When they are 

 ripe the ova have become (probably by parthenogenesis) Cypris 

 larvae, which are set free by the formation of an opening. There is 

 no parasitic castration of the host. 



,CS^MU 



Uh. 



slk. 



, Sac. 



Fig. 260. 



Fig. 260. A specimen of the shore crab (Carcinus) bearing a Sacculina. op. 

 mantle opening; Sac. Sacculina; stk. stalk. 



Fig. 261. A vertical section of Sacculina at right angles to the plane of 

 greatest breadth. From Caiman, at. atrium of oviduct; ^a. ganglion;^/, col- 

 leteric gland opening into atrium; o. eggs in mantle cavity; op. opening of 

 mantle cavity; ov. ovary; rt. roots; stk. stalk; t. testis. 



Order ASCOTHORACICA 



Parasitic cirripedia, which have an alimentary canal from which 

 diverticula extend into the mantle ; six pairs of thoracic appendages ; 

 and a segmented or unsegmented abdomen ; and are not attached by 

 the preoral region. 



These animals are parasitic and often imbedded in the tissues of 

 their hosts. They are an early branch^of the cirripede stock which has 

 retained the abdomen, in some cases well segmented and provided 

 with movable caudal rami, and has not the characteristic mode of 

 fixation by the antennules, or frontal horns in the NaupUus. 



Laura (Fig. 264), imbedded in the tissues of the antipatharian 



