The Microscope. 39 



outline (Fig. 0). The proboscis-like organ varies in length from ^^ 

 to ^^j- inch from the distal extremity of the lip, its length seeming to 

 depend upon the size of the worm that bears it. It is thick-walled 

 and hollow, and communicates with the body cavity. 



The two eyes are placed on the oral segment, one at each angle 

 of the mouth, on the ventro-lateral border. The mouth is large, and, 

 when expanded, is round, at other times showing itself as a trans- 

 verse, irregularly slit-like fissure. 



Every articulation, except the first, is supplied on the ventral 

 surface with two fascicles of podal stylets, with from three to seven 

 stylets in each cluster. In the posterior segments these appendages 

 become successively smaller and more rudimentary, until the anal 

 articulation usually has only a trace of a few short spines, or often 

 none. There is no invariable rule as to the number of stylets in 

 each fascicle, the cluster on one side often differing in number from 

 the one on the opposite border of the same segment. Frequently 

 there are only three; more than seven I have never seen in one fas- 

 -cicle. In form they are long sigmoid, terminating in a double 

 unguis, one limb of the hook being very small and inconspicuous. 

 The inner or attached end of the stylet is angularly bent and con- 

 ically tapering, the rounded enlargement common to the podal 

 spines of so many aquatic worms here usually being absent, or repre- 

 sented by a very inconspicuous swelling at the first angle. In length 

 the stylets measure from j^j to y^y inch. One spine is shown much 

 enlarged in Fig. 7. 



Beginning at the sixth articulation, and continued to near the 

 posterior extremity, the segments have on both sides a single dorso- 

 lateral bristle, usually accompanied by one or more short, straight, 

 rudimentary hairs, the former measuring from ^V to -^^ inch in 

 length, except on the extreme posterior articulations where they 

 become mere rudiments. There are none on the oral or pharyngeal 

 segments in front of the sixth body-ring. They frequently vary in 

 length on opposite sides, the short bristles being, as I suppose, 

 newly produced and in process of growth to supply the place of the 

 fully developed setpe that have been lost. Indeed, they seem to leave 

 the body with great facility, as they often fall away while the worm 

 is under the microscope, and specimens are not rarely taken with 

 the central part of the body entirely free of all appendages except 

 the podal stylets. But beginning at about the twentieth segment 

 from the posterior extremity, the bristles gradually and regularly 

 decrease in length (Fig. 4), until the anal articulation is reached, 



