TELETHUS^E. 57 



and the development of the ventral division of the foot in the anterior three or fonr, 

 as well as in the last three or four bristled segments. He places little reliance on the 

 structure of the hooks and bristles in distinguishing the species. He also examined 

 those in the Museum at Paris. 1 



The development of Arenicola Glajparedii, as subsequently stated, has been described 

 by Dr. Ashworth 2 from the ripe ova onward to the fourteenth day when only three pairs 

 of bristles were present. The larva had two eyes, and complete alimentary canal. 



Bohn 3 (1903) describes, with the aid of two text-figures, the galleries of Arenicola 

 on the beach, viz. perpendicular, sloped, and curved, and their condition in aquaria, 

 where the tubes often have but a single aperture. The galleries of Arenicola Vincenti, 

 again, occur under Litliothamnion, and it is a more sedentary form; whereas A. Grubei 

 and A. ecaudata wander considerably, the latter occasionally coming to the surface 

 surrounded by mucus and swimming freely, as Ferroniere 4 found in Cirrahdus ftliformds, 

 which, like Arenicola, shows geotropism in its tunnels, those in dry sand being vertical, 

 those in wet sand being horizontal. The author also alludes to the varieties of 

 Arenicola marina at sexual maturity. 



Bresil 5 (1903) examined the secretion of the oesophageal glands of Arenicola, and 

 found that these in an alkaline medium rapidly dissolved albuminous substances like 

 trypsin. 



Lillie 6 (1905) gave an account of the development of the nephridia in A. cristeta. 

 Amongst other features he considers the first setigerous segment as the second body- 

 somite. He traced the nephridium from undifferentiated cells of the mesoblast through an 

 early stage where the ciliated tubule opens anteriorly into the body-cavity, but not yet 

 externally, to the fully developed organ with its blood-vessels, nephrostome, and terminal 

 vesicle. They differ, therefore, from the organs of the young lava of Phoronis, in which, 

 as outgrowths of the nephridial pit, they are wholly of ectodermal origin. 7 



The statocysts or otocysts of this group have received much attention since their 

 discovery by Grube, Stannius, and Siebold, and their careful description by Ehlers, 

 Jourdan, Ashworth, and Gamble. One of the most recent researches on the subject is 

 that of Prof. Fauvel. 8 who locates the otocysts in the peristomium of A. marina, and gives 

 sections of the region in this and other species of Arenicola. He sums up by observing 

 that two species are devoid of otocysts, viz. Arenicola Vincenti and A. Glajparedii. In 

 two species the otocysts communicate with the exterior by a ciliated canal, whilst the 

 otocysts themselves have no cilia. The otoliths consist of grains of quartz from the 

 exterior, but by-and-by are covered by a secretion, the species being A. marina and A. 

 assimilis. In one species, viz. A. cristata, the closed otocysts contain a single large otolith 



1 f Ann. Sc. nat./ 9 e ser., t. x, p. 111. 



3 Arenicola, 'Liverpool Marine Biol. Committee/ p. 52, pi. viii, 1904. Vide Dr. Child, ' Archiv 

 fur Entwickelung-mechanik. der Organismen/ Bd. ix (A. cristata) ; E. B. Wilson, ' Studies Biol. Lab. 

 Johns Hopkins Univ./ ii, 1883, pp. 271—299. 



3 ' Bull. Mus. Paris/ 1903, p. 62. 



4 ( These Faculte des Sc. de Paris/ 1901. 



5 c Archiv. Zool. exper., 4 ser., t. i, p. 6. 



6 < Mitt. Zool. St. Neapel./ Bd. xvii, p. 341, pis. 22—25. 



7 Cresswell Shearer, idem, Bd. xvii, p. 487, pis. 31 — 33. 



8 ( Ann. Sc. nat./ 9 e ser., t. vi, p. 27. 



131 



