54 W. BALDWIN SPENCER. 



of the body, as said, from the vas deferens, ventral to the vesi- 

 culae seminales. The walls of the tube are thick, the cavity 

 relatively small and filled with masses of ripe sperm. The 

 walls consist of an internal layer of columnar cells, the nuclei 

 of which are small and spherical, and lie close to the inner 

 ends of the cells, which have a distinct but very thin chitinous 

 lining, forming, as noted by Stiles, folds and ridges projecting 

 into the cavity (fig. 46). External to these cells lies a clear- 

 looking tunica propria [M. P.), and external to this a peculiar 

 and strongly marked layer of muscles running in a longitu- 

 dinal direction (M. Ej. D.). In transverse sections these, as 

 Stiles says, might easily be taken for glandular structures, but 

 longitudinal sections (fig. 26, Ej. D.) and whole preparations 

 of the organ leave no doubt whatever as to their muscular 

 nature. Each separate fibre (fig. 46) is very distinct, and has 

 a general longitudinal, and at the same time slightly spiral 

 course. Each one may be described as having a stout ribbon- 

 like form, with one of its narrow edges implanted in the 

 tunica propria. The fibres thus, in transverse section, appear 

 to form a thick layer of slightly curved rod-like structures 

 radiating outwards from the tunica propria, the outer end of 

 each being slightly swollen and granular in nature, the inner 

 end clearer and more sharply defined. When the organ is 

 viewed as a whole the striations on the fibres are very evident, 

 but it is difficult to determine how they occur on the indi- 

 vidual fibres. 



(e) Cirrus Bulb (=Cirruszwiebel of Leuckart and Stiles). 

 — This is directly continuous with the vas deferens, of which 

 it may be regarded as the terminal part, whilst from its other 

 extremity the cirrus passes outwards. Its walls are thick 

 (fig. 63), and formed of some three layers of cells, which are, 

 however, very indistinctly marked in the adult, though in the 

 young stages, as in P. proboscideum, they may be clearly 

 distinguished. 



In the immature stages (fig. 63) a transverse section across 

 the cirrus bulb shows externally indications of a cavity [S.) 

 bounded by cellular walls which wrap round an internal mass 



