DESCRIPTIONS OF GENERA AND SPECIES 193 



observers to find the clitellum, may be added the fact that the clitellum, when 

 developed, is not always very obvious when the worm is examined by a lens only, 

 without subjecting it to microscopical investigation ; as I have pointed out, recently, 

 (5) the clitellum in the genus Moniligaster is unique among ' earthworms,' by reason 

 of the fact that it is only one cell thick, as in the aquatic Oligochaeta, without exception. 

 This structural fact about the clitellum, coupled with its forward position, places this 

 family in a very isolated position among the terrestrial Oligochaeta, and undoubtedly 

 affines them to many among the purely aquatic forms. A second remarkable feature 

 about this family, which now includes, besides the type genus Moniligaster, a second 

 genus described by Rosa, Besmogaster, is in the relative position of the internal 

 and external openings of the sperm-ducts ; in earthworms the funnels of these ducts 

 are always some segments in front of the external pores ; as many as eight or nine 

 segments in certain cases ; there is, it is true, a progressive series down to Allurus 

 and perhaps Tetragonurus, where the external pores are upon the twelfth segment ; 

 the funnels are presumably in the eleventh segment, though we cannot at present be 

 sure as to this, for the genus has not been submitted to anatomical study ; in the 

 aquatic forms, on the other hand, the funnels are never situated more than a single 

 segment in front of that which bears the external pore ; and there are even cases where 

 the same segment contains the funnel and bears externally the pore. This is pre- 

 cisely what we find in the Moniligastridae ; the funnel is in the tenth segment, 

 while the external pore is upon the groove separating segments x/xi. Besmogaster 

 difiers from the genus Moniligaster in the doubling of the male organs ; here the two 

 pairs of male pores are upon segments xi and xii ; the funnels of the sperm -ducts 

 are placed in the segments in front of these. The sperm-ducts communicate with the 

 exterior by means of spermiducal glands, four in Besmogaster, two in Moniligaster. 

 In Moniligaster, at any rate, the glands resemble very closely those of the 

 LumbricuUdae, and certain Tubifieidae such as Branchiura ; each consists of two 

 parts — a glandular and a muscular ; the glandular section is an egg-shaped sac, 

 which receives its sperm-duct at the extremity farthest away from the external 

 pore; it consists of a lining epithelium of low columnar cells, surrounded by a 

 layer of circularly-disposed muscle fibres, which are again surrounded by a mass 

 of granular, pear-shaped cells, with long prolongations perforating the muscular 

 layer and the lining epithelium so as to reach the lumen of the gland; the distal 

 part of the organ is chiefly muscular, with a few gland-cells interspersed among 

 the muscles, and is reflected to form a protrusible penis, very similar to that 

 organ as met with in the family Tubifieidae. It is not quite clear from Rosa's 

 account (11) how far the spermiducal gland of Besmogaster differs from that of 



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