PROBOSCIS. . 51 



fibres beneath the ciliated mucous surface, and the strong oblique and circular bands 

 (Plate X, fig. 1) form a very efficient investment. When the proboscis is about to be ejected, it 

 commences to fold over, like the turning of a finger of a glove inside out, at the point (Plate XV, 

 fig. 4, a) in front of the ganglionic commissures, a fact which has escaped most observers. In 

 withdrawal also, it may be noticed that, towards the conclusion of the process, the last wrinkle 

 of the proboscis glides within the terminal aperture, and slowly passes backwards till this 

 point is reached, when it ceases, and the organ is once more in its ordinary condition, any 

 change that afterwards ensues being due to the stretching of the shortened tube — a process 

 of simple elongation. Thus the anterior portion structurally and functionally differs from 

 the succeeding, the wall of the proboscis always intervening between it and the proboscidian 

 fluid. 



The attenuated coats of the proboscis curve outwards all round, and become fixed to the 

 wall of the foregoing canal and other cephalic tissues just in front of the ganglia ; the reflection 

 constituting the point d'appui against which the wave of proboscidian fluid impinges, when 

 the organ is about to be extruded. The thin anterior wall of the proboscis unrolls, the terminal 

 pouch is distended by fluid, and then the organ is rapidly launched forth. To judge 

 from the descriptions and drawings of M. de Quatrefages, the entire force of this liquid would 

 be thrown against the posterior part of the nerve-ganglia, and the straitened border of his hypo- 

 thetical " diaphragm" would not pass further forward. In my specimens, the waves of the 

 proboscidian fluid debouch readily into the yielding anterior canal in front of the commissures, 

 and then externally into the loop of the extruded proboscis. I have never seen the very pretty 

 lozenge-shaped arrangement of muscular bands in the snout, as figured by M. de Quatrefages, 

 and whose function, he states, is to dilate the " oral" orifice, and carry the " gullet" forward ; 

 but the elaborate stroma, shown in Plate X, fig. 3, would amply suffice for this. During the 

 motions of the proboscis, the reflection in front of the ganglia assumes various postures, and it 

 frequently does stretch obliquely forward and outward from the tube, especially when that is 

 drawn backwards. On the other hand, when the tube is thrust forward, the fibres slope forward 

 and inward. 



5. PROBOSCIS. 



I shall divide, for convenience in description, the proboscis of the Enopla into three regions, 

 viz., the anterior, middle, and posterior. The first (Plate XV, fig. 3, a) comprehends the some- 

 what cylindrical portion between the reflection in front of the ganglionic commissures and the 

 commencement of the stylet-region ; the second (b) includes the stylet-region and the well-marked 

 swelling of the great muscular reservoir; and the third (c) is represented by the long posterior 

 chamber. 



a. Anterior Hegion of the Proboscis. 



Prom the point of reflection backwards, the proboscis gradually increases in diameter until its 

 full size is attained (Plate XIV, fig. 1, and Plate XV, fig. 3), and then it remains nearly cylindrical 



