ARENICOLA ECATTDATA. 75 



tomium. Further back they are sunk in the ganglionic layer of the brain itself. In 

 specimens 6 in. to 7 in. long more numerous eyes are present. 



The proboscis of this form agrees in general structure with that of A. marina, con- 

 siderable variation occurring in the extent of the large basal series of papillae, and in the 

 coloration from pale to blackish. The large papillae at the base of the extruded organ, 

 however, have the form of small craters with an elevated rim and a depressed centre. 

 The small papillae are also proportionally larger than in A. marina, and a smooth area 

 occurs at the oesophageal infolding. 



The rings bearing feet and branchiae are broader and more prominent than the rest, 

 and they are followed by four well-marked narrower rings, the last being the narrowest, 

 and this appears to be the general arrangement to the tip of the tail, the last foot being 

 followed by a distinct ring, and then a terminal region which has a median constriction 

 so that it is more or less double. The anus is in the centre of the tip posteriorly. 



Gamble and Ashworth note that oblique muscles are absent from the anterior portion 

 of this species and A. branchialis in front of the second or third gills. Beyond this point 

 they are feebly developed. Thus the nephridia with their nephrostomes are clearly seen 

 on opening the body, and make a striking difference between them and the other three 

 species of Arenicola. 



The setigerous processes are somewhat longer and narrower than in A. marina, and 

 the bristles (Plate CHI, figs. 13 and 13 a) are much more attenuate at the tip, which 

 has a very narrow wing, the edge being minutely spinous. The whorls of spines at the 

 tip are finer and less conspicuous than in A. marina, but the essential structure seems 

 to be the same. The surface of the shaft appears to be roughened by minute spines as in 

 A. marina. 



The hooks (Plate CIII, fig. 13?)) are less robust and have a longer and more acute 

 rostrum than in A. marina, and the spines on the crown are larger and longer, one long 

 anterior spine and another above it being conspicuous. When seen antero-posteriorly 

 these appear to be double. The neck below the rostrum is boldly obliquely striated from 

 behind forward. The striated enlargement in the middle of the bristle is well-marked, 

 and so is the basal backward curve (the tip of the rostrum being in front). 



Gamble and Ashworth consider that both bristles and hooks of this and A. branchialis 

 are so nearly alike that no constant point of difference can be detected. The shaft of 

 the hook has a moderately long rostrum tapering somewhat toward its point, behind 

 which are two or three teeth. In older ones there is often a very slight process beneath 

 the rostrum. In young examples the minute hooks have two curved spines in lateral 

 view above the rostrum, and the dilatation of the shaft is marked. As these authors show, 

 the angle of the rostrum is nearly a right angle, whereas it is much greater in the adult, 

 and the rostrum itself is proportionally larger. Some present a short process on the 

 throat at this stage. The hooks of A. ecaudata and A. branchialis never attain great 

 length (Gamble and Ashworth). 



In the post-larval forms (7'2 mm. long) there are bristles with a lamina on one side 

 of the distal third or half, a short proximal region (of the lamina) devoid of hairs, and a 

 longer distal part with distinct hair-like processes, " while between the two the seta is 

 slightly constricted " (Gamble and Ashworth). This form is the Ckjmenides ecaudatus of 



