REMAKKAliU: srECIES OF ECJIIITKOIDS. 29 



The mucous nicnibrane (fig. 32, m.m. and fig. 33) constitutes 

 II moderately thick, much folded layer, which again is made up 

 of the lining epithelium {epl.) and the subjacent connective-tissue 

 layer (fig. 33, c.t.L). The former is composed of tall and narrow 

 cells containing nucleus in about the middle of their length. 

 Their internal or free end is covered with a thick cuticle (ct.), 

 while the opposite, much narrowed end seems to be directly 

 continuous with a process of the connective-tissue cell. Hence, 

 there exists no sharp demarkation of the epithelium against the 

 underlying tissue. As was noted by Jameson ('99) in Tlialassema 

 neptunij the pharyngeal epithelium incloses numerous club-shaped, 

 unicellular glands {gl.) with colorless homogeneous contents, in 

 which is observable a deeply stainable, more or less reticular 

 structure. The nucleus in these glandular cells lies always near 

 the swollen inner end. The connective-tissue layer {c.t.L) between 

 the epithelium aud the muscular layer, is of a considerable but 

 varying width. It is composed mainly of fusiform or branched 

 cells, which send out slender processes that give a fibrous ap- 

 pearance to the tissue. A quantity of variously sized, deeply 

 stainable spherules are contained in the layer ; they are in all 

 appearance the same as those found in the cutis (fig. 26, 'pg'.). 



The muscular layer of the pharyngeal wall consists of the 

 inner circular and the outer longitudinal systems (fig. 32, cm. 

 and l.m.). The latter, according to both Eietsch ('86) and 

 Jameson ('99), should be entirely wanting in Tlialassema neiduni, 

 while in Echiurus imicinctus and E. pallasi it is only weakly and 

 inconspicuously developed. In the present species, that system is 

 remarkably w'ell developed, forming a layer nearly equal in thick- 

 ness as that of the circular muscle system. 



Externally to the muscular layers is what I have called the 



