530 Miscellanea Zoologica. 



the exact resemblance of these points to the eyes of the annelidans,* 

 and from the very obvious manner in which the worms evince their 

 sensibility to the impressions of light. The species have no other 

 visible exterior organs : they move in an even continuous manner by 

 undulations, frequently imperceptible, propagated along the body, 

 which they often throw into knots and strictures, or extenuate to 

 that degree, that the ordinary breadth shall be more than four times 

 its diameter when in this state of extension. 



The internal structure is most easily seen when the worm is slight- 

 ly pressed between plates of glass, and placed under the microscope. 

 It is more beautiful and complex than the plainness and simplicity 

 of the exterior would lead us to believe, nor indeed can I unravel or 

 describe it with the accuracy that is desirable. The mouth is diffi- 

 cult to be detected, and its position and form are generally indis- 

 tinct, but sometimes it becomes evident enough, and in other cases, 

 its exact place is often shown by a slight sinus or emargination in the 

 anterior extremity in which it is placed : it is a simple circular pore 

 without any hard parts. (Plate XVIII. Fig. 5, m.) From it an intes- 

 tine descends down the centre of the body, in a straight or undulating 

 line, according to accidental circumstances of position, to the opposite 

 extremity, where it opens outwardly by a pore similar to the mouth, 

 and equally simple. The intestine (PI. XVII. Fig. 5 i. i.) is a cylin- 

 drical tube of a firmish texture, and of nearly equal calibre through- 

 out, though subject to partial and temporary constrictions and dila- 

 tations, and, as just remarked, its course can be made straight or tor- 

 tuous at the will of the animal, evidently to accommodate it to the 

 length of the body in its extreme variations, for being apparently of 

 a much less contractile tissue than the body itself, the intestine is 

 doubled in sinuous folds when the worm contracts and shortens, but 

 when this draws itself out in a long line, the intestine becomes a 

 straight canal, with something of the character and office of a verte- 

 bral column. In tracing the intestine from the mouth downwards, 

 the structure appears to be homogeneous, and alike throughout in the 

 species placed in the second section of the genus, but in the true 

 Nemertes, we meet with some remarkable peculiarities towards the 

 middle of its course. First, we perceive on each side a small cir- 

 cular spot or cavity, in each of which are three spines (Fig. 1, 2, 4,) 

 with their sharp points directed outwards ; beneath these there is 

 a cup shaped organ (Fig. 3,) encircled above with a faintly plaited 



* See Muller " sur les yeux problematiques des Annelides," in the Annales 

 des Sciences Nat. xxii. p. 19; and Grant's Outlines of Comparative Anatomy, 

 p. 252-3. 



