A NEW GENUS OF OLIGOOH^TA. 471 



On the Sth segment I found that the distance separating 

 the two ventral pairs from one another was 2| mm.; the 

 lateral pairs were separated by a dorsal area measuring 14 mm. 

 The shape of the setse is very remarkable^ and is illustrated 

 in fig. 18. Their general outline is similar to that of the 

 setae of other earthworms, but instead of terminating in a 

 hooked extremity they present a truncated appearance, which 

 will be understood by a reference to the figure cited. It 

 occurred to me, when first observing the setse attached to 

 fragments of stripped-ofip cuticle^ that they might be of the 

 normal form, but with their extremities broken off. It fre- 

 quently happens, as a result of rough usage, that the majority 

 of the setse, or at any rate a large number, are broken off 

 short ; but it is evident that that is not what has happened in 

 the present case. The free extremity of the setse showed no 

 signs of having undergone any fracture ; and, moreover, the 

 shape of the freely projecting extremity is not such as would 

 be produced by a fracture, or wear and tear. 



The setae illustrated in fig. 18 are drawn as seen on a 

 lateral view ; a and b represent the free extremities of such 

 setae more highly magnified. 



Another peculiarity in the structure of the setse is the fact 

 that their distal region, i. e. that part which lies external to the 

 slight swelling in the middle of the setse, is ornamented by 

 minute pointed processes. 



The description just given, and the figures which illustrate 

 it, refer to setse from the first ten segments or so ; but 1 have 

 ascertained that the setse in the posterior segments are abso- 

 lutely identical in size and structure with those from the 

 anterior segments. 



The first five segments of the body are entirely deprived of 

 setse j a microscopic examination of these segments did not 

 enable me to find any trace of the presence of setse. 



The disappearance of the setse from the first few segments 

 of Deodrilus, and of the species of Diachseta which I de- 

 scribed recently in this Journal (1), is a remarkable fact. 

 No other instances are at present known among earthworms. 



