NO. 1772. ANNELIDS OF THE ARENIC0LIDJE—A8HW0RTH. 



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2, The muscular pouches, a pair of which is present in several 

 species, projecting backward from the ventral region of the first 

 septum. The grade of development of these organs should be 

 noted. 



3, The nephridia, their number, the segments on which they 

 open, and, in some cases, the character of the lips of the funnel. 



4, The statocysts, when present, whether they are open or closed, 

 and the number and nature of the statoliths which they contain. 



ARENICOLA MARINA (Linnaeus). 

 =Arenicola piscatorum Lamarck. ~- 



Nineteen chaetigerous segments; thirteen pairs of gills, the first, 

 which is on the seventh segment ", may be small or absent ; gills are 

 usually bushy, but in some cases they 

 approximate to the pinnate type ; the 

 three lobes of the prostomium are 

 nearly equal in size; at any rate, the 

 lateral lobes are seldom much larger 

 than the median one; neuropodia are 

 clearly visible in each segment, in 

 the posterior branchial region they 

 form long muscular ridges, and their 

 grooves reach nearly to the mid-ven- 

 tral line ; six pairs of nephridia, which 

 open on the fourth to the ninth 

 segments;'' one pair of oesophageal 

 glands, conical or club-shaped; one 

 pair of small globular, conical, or 

 flask-shaped muscular pouches pro- 

 jecting backward from the ventral 

 region of the first septum; a pair 

 of statocysts in the peristomium, 

 which open to the exterior (the 

 apertures, which are often minute, 

 are situated close to the points where each metastomial groove crosses 

 the first interannular groove) , the numerous statoliths are composed 

 of sand grains, wliich may be enveloped to a greater or less extent 

 with material secreted by the walls of the statocyst. 



Fig. 1.— a. marina, anterior end, dorsal 

 aspect, to show tue prostomium; l, 

 lateral lobe of prostomium; l. jv, lip 



OF NUCHAL organ; M, MEDIAN LOBE OF 

 PROSTOMIUM; M. GB, METASTOMIAL GROOVE; 



Ni, FIRST notopodium; Ph, pharynx; S, 



APERTURE OF STATOCYST. X4. 



a That is the seventh chaetigerous segment. The word "segment" throughout the 

 following pages means "chaetigerous segment." The region anterior to the first 

 chaetigerous segment probably represents the peristomium and an achEetous body 

 segment, so that the first chaetigerous is really the third true segment. See the author's 

 memoir on Arenicola. Liverpool Marine Biology Committee, Memoirs, XI, 1904, p. 9. 



b The first nephridium is not uncommonly reduced or even absent. 



