9 

 ZooL.— Vol. II.] EISEN—OLIGOCH^TA. 93 



ventral side of the body. This ventral zone is quite narrow, 

 gradually increasing in width towards the tubercula puber- 

 tatis (fig. 5). 



Caudal Zone. — (fig. i.) The location of the caudal 

 zone varies considerably in different individuals, as may be 

 seen from the following table of specimens taken at random 

 from the collection from Tepic. The numerals indicate the 

 number of somites from head to zone and from end of zone 

 to end of tail, etc. 



Total. 



191 

 189 

 195 



170 

 160 

 162 



117 



212 



145 



As will be seen from the above table, the caudal zone 

 generally consists of from five to seven somites, the number 

 differing according to its location. The distance from the 

 clitellum is more constant than the distance from the tail- 

 end. The former varies from 107 to 118 somites, the latter 

 varies from 28 (or none) to 74 somites. The two specimens 

 with the very short tail may have had a portion broken off; 

 still the variation is such as to clearly show that the distance 

 to the tail-end is the least constant one. The structure of 

 the caudal zone will be referred to later. 



Tubercula Pubertatis. — (figs. 19, 20.) The continuous 

 elevated ridges constituting the tubercula pubertatis have 

 already been referred to as occupying somites ^ XIX- 

 y^ XXIII. They begin in the center of XIX and end in the 

 center of somite XXIII. Cross-sections show that this ridge 

 is a true tubercula pubertatis organ, being composed of the 

 same kind of glandular cells as are found in other genera, 

 such as Sparganophilus and Benhamia, and which have also 

 been figured by Beddard, Benham and others. There is 



