Gills of Arenicola 



57 



qI A. assimilis from. New Zealand, l)ut has not been found in those 

 from other localities. 



The dorsal axes of each gill are almost invariably the largest and 

 evidently the oldest, judging by the number of their branches ; new 

 axes are added to the gill ventrally (see PI. XIII, Fig. 43). 



Gills are not present in the genus Arenicola on the first six 

 segments ; out of some thousands of specimens the writer has seen 



Fig. 29. — A. ecaiidata. The dorsal (small) 

 and ventral (larpe) crotchets of the same 

 neuropodium of a specimen 200 mm. long. 



Fig. .30. — A . bra iic/t ialis. 

 Crotchet from a specimen 

 230 mm. long. 



only one in which a gill — a very small one — was present on the sixth 

 segment.^ In A. marina, pudlla, asdmilis var. affinis, loveni, cristata 

 and glacialis the first gill is normally on the seventh segment, in 

 A. assimilis (typical form) on the eighth segment, in A. hrancMalis 

 on the twelfth, and in A. ecaiidata on the sixteenth. In A. marina, 

 jmsilla, loveni and assimilis (including the variety) there are thirteen 

 pairs of gills ; in A. cristata and glacialis eleven pairs ; in A. hranchialis 



' One of Eanzani's specimens of ^1. clavatus {= marina) possessed a small 

 gill on the sixth segment. 



