Arenicola assimilis 



125 



Fig. 55. A. assimilis, co-type, from 

 Uschuaia. Anterior end, dorsal aspect ; 

 the prostomium is in a state of normal 

 extension. 



Tig. 56. A. assimilis var. affinis, from Otago 

 Harbour, N.Z. Anterior end, dorsal aspect ; 

 the buccal mass and pharynx are fully pro- 

 truded, and the prostomium is well extended 

 ST.O. External aperture of statocyst. 





Fig. 57. A. assimilis var. ajfinis, from the 

 Falk'and Islands. Anterior end, dorsal 

 aspect ; showing prostomium very fully ex- 

 tended, exposing to view the median pos- 

 terior part (P.), which is usually hidden in 

 the nuchal organ ; M. Median ; L. Lateral 

 lobe of prostomium ; ST.O. External aper- 

 ture of statocyst. 



Fig. 58. A. assimilis var. affinis, from Susanna 

 Cove. Anterior end, dorsal aspect ; the 

 lateral lobes of the prostomium are larger 

 than usual, but are still considerably smaller 

 than those of A. pusilla (cf. Fig. 48). 



