448 F. W. GAMBLE AND J. H. ASHWORTH. 



the fourth segment; in specimens 3 mm. to 5 mm. long in the 

 fifth segment; in older specimens 5 mm. to 10 mm. long in 

 the sixth segment ; and in adult specimens in the seventh 

 segment. 



Neuropodial Chaetse or Crotchets. — The neuropodial 

 ch^tsSj though exhibiting the same general form throughout 

 the genus^ show more variation than the capillary setae in 

 their minor characters^ not only in the different species but 

 in the same species at different ages ; hence the chaetee of a 

 given species do not present constant characters. It is, 

 therefore, difficult to determine by inspection of a given set 

 of chgetae to which species of Arenicola they belong. Each 

 crotchet consists of a shaft, generally somewhat curved, bear- 

 ing at its distal end a beak-like rostrum placed at an angle 

 to the shaft varying from about 70° to about 150°. There is 

 generally a slight dilatation of the shaft near the middle of 

 its length. Near the end of the chgeta immediately behind 

 the rostrum there are in most specimens two or more minute 

 pointed teeth, the tips of which are directed towards the tip 

 of the rostrum, while below the rostrum, at the junction of 

 the rostrum and shaft, there is often a minute process which 

 corresponds in position to the more prominent process^ or 

 tuft of hairs on the crotchets of the Maldanidae. 



The rostrum is comparatively short, and its tip is generally 

 rounded in medium-sized or large specimens, but it is larger 

 and its tip is sharply pointed in small specimens. The teeth 

 are also better developed in chastas obtained from young 

 specimens than in those from older ones. 



By careful treatment with warm caustic potash solution 

 (about 5 per cent.) the entire band of neuropodial chaetee may 

 be isolated. It may then be seen that the new chaetae are 

 formed at the ventral end of the series, the rostrum 

 being first formed, then the teeth, and finally the shaft, 

 which is at first comparatively short (see figs. 9, 18). The 

 neuropodia of young specimens contain very few crotchets 



1 In the following description the terms teeth aud process will be used 

 in the same sense as above. 



