

TUBIFEX. 363 



cavity of one part of the tube is surrounded on all sides 

 by a wall of equal thickness. This part is nearer to the 

 ciliated funnel, and its walls are thin. On the other 

 hand, the part nearer to the spermiducal gland has much 

 thicker walls, and, moreover, these walls contract a little 

 and the cavity of the tube is thrown out of position so 

 that it no longer lies centrally, but takes on the form 

 of a very open spiral, the whole tube meanwhile 

 becoming slightly shorter. If transverse sections of the 

 sperm duct were cut after its removal from the body, the 

 canal would be seen to be lying nearer the outer wall, 

 first on one side, then on the other. In sections of the 

 sperm duct cut when it is in position in the body, 

 however, the canal lies centrally for all its length, which 

 seems to indicate that the spiral curve of. the canal in the 

 first case was due to contraction on its removal from the 

 body. Beddard states in his Monograph on the Oligochaeta 

 that the coiled tube in all the members of the Tubificidae 

 is ciliated throughout, but this statement is not entirely 

 correct. In the immature form of Tubifex rivulorum 

 cilia are present throughout the whole length of the duct, 

 but the coiled tube of the mature worm can be divided 

 into two parts, one ciliated, the other non-ciliated. The 

 former lies nearer to and in connection with the ciliated 

 funnel, while the latter opens into the spermiducal gland. 

 These ciliated and non-ciliated parts of the tube can be 

 easily recognised, both in the living condition and in 

 sections. We will first confine our attention to the vas 

 deferens of the mature worm, though it will be necessary 

 later on to refer to the immature form for the purpose of 

 comparison. 



(a) T h e ciliated portion of the tube 

 occupies about half its total length, and follows 

 immediately upon the ciliated funnel (PL I, fig. 2, 



