12 



E. NOMURA 



segment, but posteriorly they lie rather in the hind region. The 

 length of a seta differs according to its position in a segment and 

 the position of the segment in the body. The dorsal setae in seg- 

 ment II are the smallest in the anterior part of the body and 

 thence the setae become larger and larger backwards for a while. 

 From segment V to the middle of the body the setae are almost 



of the same size and 



b.v 



Fig. 8. 

 Cross section through a fully grown setigerous organ 

 on the right ventral side of an anterior segment. x400. 

 c — cuticle, gc — hypodermal gland cell, s— setœ, ys — young 

 seta, hp — hypodermis, cm — circular muscle, lm — longi- 

 tudinal muscle, b.v— integumentary blood-vessel, ff — seta- 

 forming cells in follicular fundus, tm — interfollicular 

 muscle, l.mf — longitudinal parieto-vaginal muscle, t.mf — 

 — transversal parieto-vaginal muscle, n.pt — nucleolated 

 large peritoneal nucleus, n.f — nucleus of follicular cell. 



more posteriorly they 

 become gradually 

 shorter. For example, 

 in a 1 2 3 - segmented 

 specimen the largest 

 dorsal seta of segment 

 II was 77 /j. long ; that 

 of segment III, 93 a 

 in segment IV, 111 ^ 

 in segment V, 124 a 

 in segment X, 130/4 

 in segment XX, 127 

 (a ; in segment C, 37 //. 

 Moreover, as in other 

 tubificid oligochaetes, 

 the ventral setae are 

 in general larger and 

 stouter than the dor- 

 sal ; this is especially 

 ture of the modified 



ventral setae of segment II. 



The setigerous organ is of the form commonly seen in this 

 group, but as there are certain peculiarities I will give a somewhat 

 detailed description. In the follicular fundus of a fully grown 



