264 J. H. ASHWOETH. 



Arenicola, especially that of A. claparedii (Gamble and 

 Asliworth, 1900, p. 469), with which it agrees even in many 

 of its details. 



The Brain. 



The brain is lodged in the middle portion of the pro- 

 stomium (fig. 15). It is somewhat A-shaped, the single 

 anterior lobe being in contact with the anterior face and 

 dorsal wall of the prostomium, and the two posterior lobes 

 lying in contact with the inner sides of the two nuchal 

 grooves. In some specimens the anterior brain-lobe is not 

 in close contact with the dorsal prostomial epithelium along 

 its whole length, but in the posterior half is separated from 

 the epithelium by a thin sheet of muscle-fibres. The brain 

 is placed in a slightly slanting position, its anterior lobe 

 being situated more dorsally than the posterior lobes. 



The anterior lobe is almost entire, the only trace of division 

 being a very slight groove along its ventral surface ; but the 

 two posterior lobes of the brain are separated from each 

 other by a considerable space lined by coelomic epithelium, 

 and containing muscle-fibres and blood-vessels. 



The dorsal and lateral portions of the anterior brain-lobe 

 consist chiefly of small oval or pyriform cells, some with 

 small deeply-staining- nuclei, others with vesicular nuclei, 

 with one or two small dark nucleoli. A few larger cells are 

 found here and there. The ventral part of this lobe of the 

 brain consists chiefly of a delicate neuropile. 



The anterior brain-lobe gives off a pair of moderately stout 

 nerves to the hollow tentacles {N. Tent., fig. 15). The nerve 

 spreads out just beneath the epidermis of the base of the 

 tentacle, gradually thinning out towards the tip. The stout 

 oesophageal connectives arise from the brain a little further 

 back, i. e. about the middle of its length. The tentacular 

 nerves receive fibres from the dorsal and ventral part of the 

 anterior bi'ain-lobe, and there is a considerable mass of cells 

 immediately below and to the outer side of the origin of each 

 of these nerves. The connectives also receive fibres from 



