138 FIELD AND FOREST. 



together. The former then appears as a single bundle of long fibres, 

 and the latter as a plano-convex mass with four prolongations, two of 

 origin and two of insertion. In one specimen it was my pleasure to 

 examine, there was, however a different arrangement, the only instance 

 of the kind I have met with after many examinations. In this case 

 both sets of muscles were entirely free. The setigerous masses were 

 distinct and separate. The two transverse bundles on each side of 

 each segment crossed from one row to the next, connected together 'so 

 delicately that a few touches of the needles parted them. By them, 

 seta number one in the lateral row was joined to seta number two 

 in the ventral on each side of the median line and counting toward it, 

 it and seta number two in the lateral to number one in the abdom- 

 inal, apparantly a complicated arrangement, but really simple. 

 They were directly attached to the setae, so that when the lat- 

 ter were extracted the muscles became tense and were finally rup- 

 tured. As has been said this is the only instance of the kind I have 

 seen. The infrequency of the arrangement, at least in my own ex- 

 perience, must be my only excuse for this somewhat lengthy, and 

 perhaps dry description of a seeming anomaly. 



Down the back of the creature, in the middle line, one in each inter, 

 segmental ring, is a row of circular openings. On the inner surface of 

 each segment, therefore below the longitudinal muscle, is a muscle 

 parallel with the length of the worm, and extending from the lower edge 

 of the orifice above to the upper edge of the aperture below. The 

 two ends are thickened vertically and slightly broadened, whence they 

 gradually narrow toward the centre. What the use of the openings 

 may be, it is impossible to conjecture. They seem to have no connec- 

 tion with any of the internal organs, but to form a direct communication 

 between the external air and the general cavity. The function of the 

 muscles is evident. By their contraction they must widen the orifices, 

 naturally found closed and invisible until pulled open by needles on 

 the stage of the microscope, in imitation of the muscular action. 



The six anterior segments contain a distinct muscular system. 

 Numerous bundles of long fibres take their origin in one chamber, 

 pass through the septa and are attached to the next segment, while on the 

 sides and near the ventral surface there appear to be several sets of three 

 or more, radiating like the frame work of a fan from points near to- 



