194 Introduction to Animal Morphology. 



petition. The surface may be naked or loricated, the 

 lorica being either closely applied or as a loose sheath. 

 At the anterior end lie one or more ciliated, lobate 

 discs (homologous with the anterior ciliary zone of the 

 larvae of Echinodermata, Gephyrea, &c.), the motion 

 of whose (usually double) rows of cilia gives the ap- 

 pearance of rotating wheels. Between the cilia are 

 long, stiff bristles, and inNotommata centrura a cluster 

 of such bristles lies in the centre of the body. Beside 

 these trochal discs there is often a ciliated, frontal lobe 

 (calcar or antenna, double in Melicerta), and there 

 may be a ciliated, dorso-ventral groove on the surface. 

 The dermis is of finely granular protoplasm, with a 

 layer of round cells like the parenchyma cells of Tur- 

 bellarians. Under this is an interrupted muscular 

 layer of circular and longitudinal, smooth or striped 

 fibres, often divided into bands, which may be spe- 

 cialized for the contraction of the body (which they 

 sometimes draw in like a telescope), and retraction of 

 the trochal disc. 



There is one cervical nerve-ganglion, often in 

 symmetrical halves, lying on, not around, the pharynx, 

 giving off branches to the eyes and bristles, as well as 

 lateral body-filaments. The eyes are one or two, red, 

 placed on the neck or forehead ; when only one there 

 is rarely, when tw^o there are usually, lenses and 

 nerves connected therewith. Some have eyes in the 

 embryonic, and lose them in the adult, state. Touch- 

 bristles may be placed around the frontal lobes or 

 trochal discs, and one or two conical or cylindrical, 

 hair-beset tentacles may be placed on the neck. On 

 the ganglion lies a sac containing a white, chalky 

 matter, with, in a few cases, a duct apparently opening 



