HABITS OF RHABDOCOELIDA 



45 



which occurs in the lacunar spaces and alimentary canal of young 

 shore crabs (Carcinus maenas), is a white cylindrical animal 

 - inch long, with a red snout. After attaining maturity it 

 works its way out of the crab and encysts under stones, 

 forming a pyriform mass in shape like a " Prince Rupert's drop." 

 Within this case the eggs develop, and the young probably 

 emerge through the open nar- 

 row end of the hard white 

 tube, biit how they reach the 

 crab is not known. Graffilla 

 muricicola is found in the 

 kidney of Murex brandaris and 

 M. trunculus, at Naples and 

 Trieste ; G. tcthydicola in the 

 foot of Tethys. Anoplodium 

 parasiticum occurs among the 

 muscles which attach the 

 cloaca of Holothuria tubulosa 

 to the body - wall ; and A. 

 schneideri occurs in the sea- 

 cucumber, Stichopus variegatus. 

 These are truly parasitic forms, 

 constituting a special sub- 

 family. They have no rhab- 

 dites in the skin ; the nervous 

 system and sense-organs are w 



only slightly developed; and Fw . 19< _ FormsofRhaMocoeH(la . \ M ^. 

 the pharynx has undergone a 

 notable reduction in relation 

 to the simpler mode of obtain- 

 ing nourishment. Other cases 

 of association between certain 

 Rhabdocoels (closely allied to, 

 if not identical with, certain 

 free-living species) and Lamellibranchs or Sea-urchins, are, how- 

 ever, of another kind. Thus on the gills or in the mantle 

 cavity of species of Mytilus, Cyprina, Tellina, and upon the 

 test of Clypeaster, such forms as Enterostoma mytili, Acmostoma 

 cyprinae, and Provortex tellinae have been found. But it is 

 probable that these Turbellaria here obtain merely a temporary 



stwna tetragonuiii O. F. M. (Rhabdocoela), 

 x 10 ; B, Convolutaparadoxa Oe. (Acoela), 

 x 10 ; C, Vorticeros auriculatum 0. F. M., 

 x 6 ; D, Monotus fuscus Oe. (Alloeocoela), 

 x 4. ap, Adhesive papillae ; d, intestine ; 



MI, pharynx ; ot, otolith ; rh, rhabdites ; 



te, testes ; ut t uterus with eggs ; yg, yolk- 



glands ; <J, male, 9, female genital pores. 



(A after Brauu.) 



