HABITS OF RHABDOCOKLIDA 



45 



which occurs in the lacunar .spaces and alimentary canal of young 

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

 I inch long, with a red snout. After attaining maturity ii 

 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, but how they reach the 

 era!) is not known. Qraffilla 

 murieicola is found in the 

 kidney of Murex bvandaris and 

 M. truuculus, at Naples and 

 Trieste ; G. tcthydicola in the 

 foot of Tetliys. Anoplorfi H m, 

 jHnasiticum occurs among the 

 muscles which attach the 

 cloaca of Holothuria tuhulosci 

 to the body - wall ; and A. 

 achneideri occurs in the sea- 

 cucumber, Stichopii8 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 

 only slightly developed ; and ^ 1Q 



A c d 



Forms of Jthabdocoelida. A. 



ttoma Utragowwai 0. F. M. (Rhabdocoela . 

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

 xlO; C. Vorticero8 auriculatum 0. F. M.. 

 x 6 ; D, Monotuafutem Oe. (Alloencoela). 

 x 4. op, Adhesive papillae ; <I, into 

 in, pharynx ; ot, otolith ; rh, rhabditon : 

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

 glands ; S, male, 8, female genital pores. 

 (A after Brauu.) 



the pharynx has undergone a 

 notable reduction in relation 

 to the simpler mode of obtain- 

 ing nourishment. Other cases 

 of association between certain 

 Bhabdocoels (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, Telltna, and upon the 

 test of Clypeaster, such forms as Enteroston\ mytUi t Acmostoma 

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

 probable that these Turbellaria here obtain merely a temporary 



