520 J. PERCY MOORE. [Vol. X. 



somite five, both being usually displaced to the left side by the 

 spermatheca, which occupies the right of the same somite. 

 Penetrating the septum 5-6 close together near its ventral 

 attachment, they unite, and proceed as an unpaired duct to the 

 copulatory bursa, to the anterior walls of which it is attached, 

 and then turns sharply upward to empty into the middle of the 

 glandular sperm reservoir. The posterior pair, lying entirely 

 in somite six, are shorter and more symmetrically arranged. 

 Their free ends are attached to the anterior face of the septum 

 ^-y, from which their mouths turn forward. The common 

 duct into which they unite is slightly attached to the bursa, 

 and empties into the sperm sac at the same place as the 

 anterior (Fig. 19). These vasa deferentia are rather broad 

 thick-walled tubes with narrow lumens. They are lined by a 

 naked cubical epithelium, which becomes more columnar and 

 acquires cilia a short distance from the free end, which presents 

 no funnel-like expansion. (In a single preparation, out of a 

 great many examined, all four vasa deferentia possessed ex- 

 panded mouths.) The epithelium is covered by an outer layer 

 of narrow elongated cells, which are placed transversely, and 

 form a complete investment around the duct, except of the 

 ciliated cells, which extend freely beyond this covering (Fig. 

 25). These cells are undoubtedly muscular, and have the 

 same structure as the larger muscle fibres which similarly 

 invest the walls of the spermatheca (Fig. 21). In living ani- 

 mals subjected to pressure a faint and irregular wave of con- 

 traction may sometimes be seen to travel along the walls of a 

 vas deferens toward the atrium ; and such peristalsis doubtless 

 serves to impel the spermatozoa along the non-ciliated passages. 

 The atrium (Figs, 19 and 20) or enlarged terminal portion of 

 the male efferent apparatus, is divided into two distinct por- 

 tions, the internal glandular spermatic vesicle, which belongs 

 to the vasa deferentia, and serves to collect and retain the 

 spermatozoa; and a prominent muscular-walled region which 

 functions as a copulatory organ, and is derived from an invagi- 

 nation of the body walls. The former (Figs. 19 and 20, sv) is 

 a short curved sac, somewhat enlarged at the free end and 

 tapering toward the other, where it suddenly contracts in 



