54 ILLIXOIS BIOLOGICAL MONOGRAPHS [334 



situated between the large flask like ends of the collecting ducts and 

 the pore. In the pulsations of this organ, the anterior ventral part 

 contracted and the constriction passed posteriad and dorsad, expelling the 

 fluid thru the pore. The two collecting ducts extend cephalad from the 

 excretory vesicle, one on either side of the forebody, median to the vitel- 

 laria. Just posterior to the pharynx each duct divides, sending a branch 

 cephalad on the lateral side of the pharynx and anterior sucker, and a 

 second branch turns caudad. This caudal branch subdivides into a 

 branch leading to the region of the genital pore, and a longer larger 

 branch which passes posteriorly to the region of the testis and receives 

 many smaller side branches. Cross sections (Fig. 49) show the collect- 

 ing ducts to be dorsal in position. In morphological and histological 

 features the excretory system of C. cokeri is similar to that of C. insig- 

 nis. Osborn gives a comparison of the excretory system in that species 

 with the same system in other genera of the family. 



Sensory Structures. — There is a dorsal nerve commissure crossing 

 the anterior part of the pharynx, and nerves were traced running ceph- 

 alad and caudad from it. In about half of the specimens mounted in 

 toto, a pair of black pigment spots is present on the dorsal commissure. 

 In others only a single spot is visible and in a few specimens none could 

 be found. In all the sectioned worms, however, both "eye spots" were 

 observed, altho in some they were very small and difficult to find. These 

 structures are dorsal and anterior to the pharynx (Fig. 58) and consist 

 of a large number of black pigment granules. No lens is present. 

 Barker and Parsons report that eye spots were not found. 



At the ends of the cross partitions of the adhesive disc are the mar- 

 ginal organs (Fig. 55). These structures occur in the interstices be- 

 tween the muscular ridges of the ventral disc and its peripheral wall. 

 Such an organ consists of a fine tube about 20^ in length and Ifx in di- 

 ameter, leading dorsad from the ventral surface of the ridge and termi- 

 nating in a large spherical cavity in the form of a bulb. The entire or- 

 gan is lined with cuticula, continuous with that of the external surface 

 of the body. The external half of the canal possesses a thick wall com- 

 posed of annular muscles, while the internal portion has a thin wall with 

 a few annular fibers and is often curved or looped. At the external end 

 of the inner portion there is a flask-like enlargement which is connected 

 with the heavy walled region by a short constricted portion about 2/jl in 

 length. Longitudinal fibers pass from the wall of the distal part of the 

 canal to points near its inner end or to the wall of the cavity. This lat- 

 ter structure is spherical or oval 15 to 20/x in diameter, and empty in 

 most of the sections. It has a fibro-membranous wall and in a few cases 

 is filled with homogenous granular substance or fluid. In other sections 



