623 



Penial Bulb. — In many respects the structure of the penial bulb 

 (PI. C, Fig. 20) in this species is similar to that of F. iirma, although 

 a number of distinct differences are apparent. Unlike that of the 

 latter species the body of the Imlb is composed of cells of but one 

 kind. They are large and glandular, and each contains a large, con- 

 spicuous nucleus at the peripheral end. Each cell has a prolongation 

 which extends to the penial lumen. The peripheral part of the cell 

 stains deeply but the prolongation stains only very slightly. The 

 sperm duct enters the bulb at the anterior end and extends obliquely 

 ventrad, opening into the penial lumen. Figure 20 shows the struc- 

 tural detail of this organ as it appears in a transverse section of the 

 worm. This bulb is clearly of the lumbricillid type as defined by 

 Eisen. It differs from that of F. firma in lacking the inner bulb cells 

 which surround the penial lumen. 



Spcrntafhcccc. — Each spermatheca (PI. C, Fig. 21) is differen- 

 tiated into ampulla, duct, and several diverticula. The ampulla is 

 somewhat elongated and inflated in the middle. The ectal end bears 

 a circle of globular sessile diverticula, usually seven in number and 

 slightly dissimilar in shape and size. The duct arises from the center 

 of this circle of diverticula and extends, with few curves, to its 

 ectal opening in the lateral wall of the body slightly posterior to 

 IV/V. Two pear-shaped glands are present at the ectal opening. 

 The cuticula is reflected into the lumen of the duct and lines it for 

 its entire length. 



Fridericia AG11.IS Smith 



At the time that this species was described*, certain organs of the 

 Bnchytrccidcc were not considered of as much systematic importance 

 as at present, and, accordingly, they were ignored, or received scant 

 attention in the description of 7^. agilis. In view of the large number 

 of species of the genus already known and of the large number that 

 are almost sure to be made known in the future, it is important that 

 descriptions should be quite detailed. For this reason an examina- 

 tion of additional material and a further study of old material have 

 been made and a more extended description prepared, no attempt 

 being made to distinguish the old material from the new. 



JDcfinition. — Length, 25-30 mm. Diameter, 0.63-0.82 mm. 

 Somites, 57-66, average, 62. Color, whitish. Prostomium blunt and 

 rounded. First dorsal pore in VII. Setre, 2-4, usually 2, per bundle. 

 Clitellum on XII-XIII. Lymphocytes numerous, broadly elliptical. 



*In 1895, in the Bulletin of the Illinois State L^aboratorj of Natural His- 

 tory, Vol. IV, Art. VIII, pp. 288-289. 



