The Arenicolidce of South Africa. 1 



on the left side there is a corresponding setal sac, but setae are no 

 longer present in it. The setae remaining in this specimen are now 

 very loosely held in position, several bundles of notopodial setae are 

 seen to be on the point of falling out of their setal sacs and others 

 have already dropped out, including the small tuft which was in 

 the twentieth left notopodium. 



There is no trace of neuropodia or neuropodial setae or of gills on 

 either side of this twentieth segment. 



The type specimen is, therefore, abnormal in that it possesses an 

 additional chaetigerous segment, but this extra segment is not pro- 

 vided with fully developed parapodia ; its notopodia are smaller than 

 those of the preceding segments, and it possesses no neuropodia. 

 Kinberg's figure is correct in its representation of this extra seg- 

 ment. There is such a remarkable constancy in the number 

 of chaetigerous segments in the caudate species of Arenicola that 

 the presence of an extra pair of notopodial setal tufts in Kinberg's 

 figure called forth Professor Fauvel's remark that this might be 

 due to an error of observation. Cases in which extra notopodia, 

 neuropodia, and gills are present in caudate Arenicolidae are rare. 

 Among some thousands of specimens of A. marina which have 

 passed through my hands during the last few years, I have seen 

 only three * with a complete chsetigerous and branchiferous twentieth 

 segment. Out of over one hundred specimens of A. cla'paredii 

 examined, I have seen only one which exhibits an abnormality of 

 this nature ; this specimen has an extra (twentieth) notopodium and 

 neuropodium, but on one side only. 



Neuropodia are clearly visible on all the chaetigerous segments of 

 A. loveni. On specimen No. 4 the groove of the first neuropodium 

 is about 1 mm. in length, that of the second 2 mm., of the third 

 4 mm., of the fourth 7 mm., and of the fifth, sixth, and seventh 

 12 rum. The groove thus exhibits a rapid elongation in successive 

 segments until in the fifth, sixth, and seventh segments it attains 

 its maximum length of about 12 mm., and almost reaches the mid- 

 ventral line. The right and left neuropodial grooves in this region 

 of the body are separated ventrally by a distance of only a little over 

 1 mm. In the following segments the neuropodial grooves are 

 slightly shorter, they gradually diminish from 11-5 mm. in length 

 in the eighth segment to 9'5 mm. in the nineteenth segment. The 

 neuropodia of the first few segments are scarcely raised above the 

 general surface of the chaetigerous annulus, but those of the tenth and 

 succeeding segments are clearly seen as elongate ridges, extending 



* Not seven, as erroneously stated in Arkiv for Zoologi, Bd. 7, No. 5, p. 7. 



