DESCRIPTIONS OF GENERA AND SPECIES 601 



behind the first are thickened, and formed of two distinct layers of fibres ; the last 

 of the thickened septa separates segments xi/xii ; the next septum, however, although 

 not so thick as those which precede it, is thicker than those which follow. 



Another character, which at present distinguishes the present genus from any other, 

 is the formation of separate chambers for the setae. A membrane shuts off the area 

 occupied by the septa from the rest of the body-cavity; this condition is only 

 paralleled among the Capitellidae. 



The alimentary canal of Libyodrilus differs from that of other Eudrilidae in 

 having no glandular appendages to the oesophagus. There are three gizzards, which 

 lie in segments xxiii-xxv, one gizzard to each segment. The intestine has a typhlosole ; 

 this is of rather a peculiar form ; from its commencement to about the thirty-seventh 

 segment three folds can be seen on dissection ; the middle one is about three times the 

 diameter of the two lateral folds ; after the thirty-seventh segment the two lateral folds 

 disappear. 



The testes are two pairs in the eleventh and twelfth segments respectively ; they 

 are quite unenclosed by the sperm-sacs. The sperm-sacs are in the eleventh and 

 twelfth segments. Each sac is independent of its fellow ; the sperm-ducts are also 

 unenclosed by the sperm-sacs ; nor is there any dilatation of the duct near to the 

 funnel, such as is met with, for example, in the genus Eudmlus. The funnels of the 

 sperm-ducts, moreover, face forwards, as in the majority of Oligochaeta; they do not 

 depend from the anterior wall of their segments (the tenth and eleventh) as in many 

 Eudrilidae. The spermiducal glands have the tubular form which is met with in all 

 the Eudrilidae. They are particularly short, and open by a common aperture ; the 

 spermiducal glands have a thick muscular wall ; with each is connected a sac 

 containing a single short penial seta ; this seta is quite unornamented ; the sperm- 

 ducts retain their distinctness up to the point of opening into the glands ; they 

 appear to open into the gland close to its external orifice ; but, as a matter of 

 fact, they pass up within the thickness of the muscular layer of the organ, and 

 actually open into its lumen quite at the summit ; the lining membrane of the 

 spermiducal gland is greatly folded. 



A large sac lies upon the dorsal surface of the oesophagus 1 , extending from the 

 anterior boundary of segment xiii to the posterior extremity of segment xviii. This 

 sac gives off on either side three diverticula ; anteriorly the sac divides so as to 

 embrace the oesophagus, and again to surround the nerve-cord. This sac contains 

 spermatozoa, and is the physiological equivalent of the spermathecae of other eartb- 



1 On p. 134 will be found a more detailed description of the structure and development of this sac. 



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