BHABDITE-OELLS IK CEPHA.LODISCUS. 267 



divided into Mocks. Burger * describes other homologous bodies 



Nemertea as flask-shaped gland-cells. 



According to these descriptions there can be little doubt that 

 the bodies described in this paper are similar, in all their essential 

 points of structure and development, to the rhabdites, pseudo- 

 rhabdites, &c. of Turbellaria and Nemertea. We have in fact 

 a complete and gradually ascending series commencing with the 

 comparatively simple cells in Nemertea, and terminating in the 

 complex structures of Cephalodiscus. In GepJinlodiscus they are 

 more differentiated (1) as regards accessory secretions in the 

 cells ; (2) as regards the details of the development of the rhab- 

 dites ; and (3), provided the view stated in this paper be correct, 

 in th.e separation of the portion containing the secretion from 

 the mother-cell, so that the two become quite distinct. 



Stjmmaky. 



GepJialodiscus lias a lophophore of 12 branchial plumes, each 

 of which consists of a central stem or axis with its associated fila- 

 ments. Each axis becomes enlarged at its distal or free extremity 

 so as to form a conspicuous hollow bulb, the cavity of which is 

 continuous with the cavity of the stem. As the rhabdite-cells 

 are entirely confined to these bulbs, the latter may be con- 

 veniently termed rhabdite-batteries. Histologically, the wall of 

 the battery is greatly vacuolated, and contains essentially two 

 series of bodies : (1) a series of large nucleated basal cells ; 

 (2) above these a series of non-nucleated bodies lodged in the 

 vacuoles and termed rhabdite-" cells." 1 and 2 together, how- 

 ever, are the equivalent of a rhabdite-cell of a Turbellarian, 

 since 2 possesses no nucleus, and 1 contains no secretion. In 

 fact 2 must be regarded as a disassociated portion of 1. The 

 secretion of 2 is primitively a large homogeneous sphere. 

 This may or may not become fragmented. Subsequently there 

 often arise two small aster secretions of unknown origin, fate, 

 and significance. The sphere of secretion afterwards splits 

 peripherally so as to form, first a star-shaped structure, and then 

 a number of stout free rods. The splitting usually leaves a 

 residue, but the whole of the sphere may be used up in the 

 formation of the rods. The rods have been observed arranged 

 in a definite bundle parallel to the long axis of the " cell." The 



* Bi'onn's Thier-reichs, Bd. iv. 



