1010 NOTES OX AUSTRALIAN EARTHWORMS, 



ments are indicated but are less developed, the depression not 

 extending so far from side to side, its margins not so tumid, and 

 its shape not so well-defined, and lying closer to the anterior than 

 to the posterior margin of the segment. On the other hand as 

 some specimens have the ventral surface convex but thickened for 

 a space outwards on each side as far as about the second row of 

 setae, the thickening most marked towards the ends of the thickened 

 area (which sometimes is dumb-bell-shaped from the extremities 

 encroaching a little) it may be that the depression referred to is 

 only or chiefly post mortem and due to the unequal contraction of 

 a not uniformly thickened surface. Out of about 100 (spirit) 

 specimens by far the majority of them show at least some indica- 

 tion of it. Individual variations in detail are common, and very 

 frequently in the median line just behind the anterior margin of 

 the segment there is one or a pair of dots or pits on a more or less 

 distinctly thickened area resembling the accessory copulatory 

 structure, or there may be one median, and two lateral dots or 

 pits, in front of the ^ papillae. The supposed accessory copulatory 

 structures vary in number, situation, and in pattern and size 

 according to the extent to which they are developed. The first 

 indication of each of them in immature worms is a pair (or there 

 may be only one) of circular translucent dots or pore-like pits in 

 the intersegmental groove (except in the case of those on the 

 ventral surface of xviii) one on either side of and not far from the 

 median ventral line ; on each side of the intersegmental groove a 

 portion of the ventral surface of each segment becomes modified 

 forming a lanceolate or nearly elliptical transverse thickening 

 extending from the innermost (ventral) row of setae on one side 

 across the median ventral line to the innermost row of the other 

 side, and from before backwards extending over one or part of one 

 annulus or more of each pair of segments between which it occurs, 

 the surface still completely traversed by the intersegmental furrow, 

 or a portion of the latter completely enclosed ; in more mature 

 individuals the thickening increases, the pattern of the whole 

 structure becoming more definite (lanceolate or nearly elliptical), 

 the surface shallowly concave with an enclosing raised rim, or the 



