1900.] EARTHWORMS OF THE GENUS AMTNTAS. 611 



presence of additional sperm-sacs in segment xiii., and even in x., 

 seems to be distinctive of a few species ; but here it is not certain 

 that variations do not occur. 



There are next to be considered a number of characters which 

 will probably be of use when they are better known. At present 

 they have to be used with great caution, and cannot be much 

 respected unless they are based upon the examination of a large 

 number of individuals. 



(1) The Genital Papillae. — It does seem that there are species 

 (e. g. A. padasensis) in which these structures are entirely absent. 

 But they appear likewise to be occasionally absent from specimens 

 of species which normally possess them. In a few forms they are 

 very constant in number and arrangement. In A. posthumus, for 

 example, there are two pairs always (except in obvious asymmetrical 

 monsters) in the same place. But elsewhere they vary enormously. 

 To give one instance : I have examined many specimens of the 

 common i. heterochcetas, and oulyonce have I found a pair of small 

 papillae in front of and behind the spermathecal pores, a common 

 enough position for such papillae in other species. 



(2) The relations of the Spermatheca to its Muscular Duct. — 

 Sometimes, as in A. forbesi and A. imjmdens, it is easy enough to 

 distinguish the relatively large thick duct from a duct which 1 is 

 practically absent, the pouch being almost sessile. But other 

 cases come so near to each other, and the amount of contraction 

 may be so different, that the character is not always of practical 

 value. The same is the case with the diverticulum. The long 

 spirally-wound accessory pouch of A. musicus cannot be confounded 

 with the rudimentary knob of A. iris; but the middle examples 

 of the series cannot be so easily defined, and in most cases cannot 

 be distinguished at all. The occasional existence of accessory 

 diverticula upon the main diverticulum does not appear to be 

 constant. Rarely (A. ijimce) there is no diverticulum ; but it 

 would be more satisfactory to be assured on the results of section- 

 cutting that the absence is real and not merely apparent. 



(3) The length, thickness, and degree of curvature of the 

 muscular duct of the glandular appendage of the sperm-duct is 

 apparently a character of value ; but, again, it has to be used with 

 caution, chiefly because the descriptions extant are not always clear 

 upon the point. Also the shape of the gland itself. This, how- 

 ever, does appear to vary considerably in degree of lobation and 

 in size in the same species. 



(4) A fourth character which must be used with caution is 

 the extent of the clitellum. Not indeed those cases where it 

 extends beyond the normal segments, but its actual line of com- 

 mencement and ending upon the xivth and xvith segments. It 

 certainly varies a little in the same species. 



(5) It is quite possible, when more is known about the facts, 

 that the point at which the sperm-duct becomes confluent with 

 the duct of its terminal gland will prove to be a character of 

 importance. 



(6) An ornamentation of the setae has been observed in A. hetero- 



