76 ANATOMY OF THE ENOPLA. 



fessor Keferstein's notice of the organ in (Erstedia pallida is very brief ; and he has abstained 

 from figuring its relations, though affirming that its opening (constituting the mouth) is on the 

 ventral surface behind the ganglia, as in the Anopla. M. van Beneden, while indicating an 

 outline of the structure in Folia cajpitata, makes no reference thereto in his descriptions. The 

 same omission is made by M. Claparede in regard to his figure of ProsorhocJimus Claparedii. 



In all the Enopla the oesophageal organ is easily observed (Plate XIV, fig. l,j) as an elongated 

 structure, occasionally tinted of a pale reddish brown colour, slightly narrowed posteriorly, and 

 usually thrown into various longitudinal wrinkles. It diminishes somewhat abruptly behind the 

 ganglionic commissures, and passes forward beneath the inferior one to the oral aperture at the 

 ventral border. The narrow anterior channel for the proboscis lies close above the oesophagus 

 towards the anterior part of the snout (Plate X, fig. 3). The two tubes become more 

 evidently separated in most sections just in front of the ganglia, and the interposition of 

 the broad inferior commissure soon renders the distinction more apparent (Plate XV, fig. 1) ; 

 thereafter they have the tunnel of the proboscis as a party-wall, together with that portion of the 

 extra-proboscidian region in which the median blood-vessel is situated. The oesophagus, more- 

 over, occupies a special chamber, bounded by a series of well-marked fibres (Plate XI, fig. 2, 7c) y 

 which pass downwards from the upper wall by the side of the proboscidian sheath, and unite in 

 the median line below it. The anterior narrow portion is translucent, and close behind the com- 

 missure a wrinkled arrangement is often seen, which is followed by the more opaque portion with 

 its deep longitudinal rugae. The former appearance is very similar to that which is caused by tying 

 the mouth of a leather bag, and is due to the glandular folds and constriction of the organ in front. 

 The pale division behind the ganglia shows active ciliary motion, but there is no trace of an aperture; 

 indeed, the great and peculiar stretching of this pale portion, as it is dragged backwards from the 

 region in front of the ganglia, at once demonstrates the fallacy of supposing it connected with any 

 post-ganglionic aperture. The wall of the organ evidently contains some contractile circular 

 fibres, which cause it to dimple inwards here and there during its motions ; and in anterior trans- 

 verse sections the ends of longitudinal muscular fibres are distinctly shown, though they are 

 finer than those of the proboscis. Posteriorly the oesophagus opens into the alimentary cavity; 

 but the communication is not actually seen in ordinary views, and I have not been able to observe 

 the animals feeding. 



The wall increases in thickness after passing the narrow portion in front, and again slightly 

 diminishes posteriorly. In transverse sections of specimens hardened in spirit and mounted in 

 chloride of calcium the structure has a streaked and fibrillated aspect (Plate XIV, fig. 12), being 

 marked by a series of vertical striae, and minutely granular, an appearance due to the position of 

 the glandular follicles with respect to the inner surface, and the change caused by the preparation. 

 It will also be noticed that in these sections the structure is thrown into numerous characteristic 

 longitudinal folds. In the living example the inner edge of the organ (Plate XIII, fig. 20, a) has 

 a somewhat translucent and well-defined border, garnished with moderately long and most 

 vigorous cilia ; indeed, the latter and the wall retain their irritability a considerable time after 

 the death and partial decay of the animal, just as Darwin and Duges observed in the proboscis 

 of Planaria. The inner surface in the fresh specimen is always thrown into numerous wrinkles, 

 and crossed by pale streaks — the ciliated edges of the folds (b). The entire structure is studded 

 internally with a series of granular glands or follicles, which taper towards the free ciliated edge 

 of the rugae, and numerous brownish pigment-granules. 



