752 J. TT. AsiiworxTn. 



Sense Org'ans. — Tlie eyeSj of which there are four or five 

 on each side of the prostominm, are simihir to tliose of other 

 Arenicolidas (Gamble and Ashworth, 1900, ])p. 500, 507). 

 They are situated either among the small nerve-cells on the 

 dorsal surface of the anterior cerebral lobes just in front of 

 their point of union, or in the epidermis immediately dorsal to 

 tills region. Each eye is composed of a cup-shaped mass 

 (G to 12 fx in diameter) of reddish-brown pigment spherules 

 grasping the base of a spherical or ovoid leus. 



The otocysts ^ are remarkable for their large size. They 

 are oval sacs whose three internal diameters are o7, O'oG, and 

 0'25 mm. respectively. Their size may })e better appreciated 

 sifter comparison with that of the otocystii of other species 

 (see figs, lo, 16). The largest otocysts seen while examining 

 four large specimens of A. marina for this purpose were 

 found in one about 180 mm. long, where they measure 0*07, 

 0T6, and 0"17 mm. along each of their three internal dia- 

 meters ; Avhile in a specimen 250 mm. long the corresponding 

 measurements are OTo, 012, and 0*15 mm. (fig. 10). The 

 nearly spherical otocysts of full-grown specimens of A. 

 cristata (300 mm. long), A. grubii (180 mm.), and A. 

 ecaudata (180 rum.) have a mean internal diameter of 

 0T7 to 0-18 mm., OTO to 0T7 mm., and 12 to O'lo mm. 

 respectively. From these figures it will be seen that the 

 otocysts of A. assimilis are much larger than those of 

 any other species. Each opens to the exterior by a narrow 

 curved tube. The external opening is very minute, and at the 

 bottom of a groove situated immediately in front aiid to the 

 outer side of the lateral portion of the nuchal organ (lig. 22). 



• Elileib (lyul, ))p. 177, 17S) lias recently dehcribed lliese organs :uk1 their 

 numerous splierical otoliths, consisting of a concenliieally layered, evidently 

 secreted, nniterial. These vary in size from 0003 to Oo nun. The small ones 

 arc compared lo those of A. claparedii (the aulliur really means A. grubii). 

 Tiie larger otoliths are often irregular, and in a few a central foreign body may 

 be observed. The opening of the tube into the cyst is very small, and Ehlers 

 thinks this is correlated with the character of the otoliths, lie also slates 

 thai liie olocysl is ai)parenlly larger and its external o])eniiig nearer Uie 

 braiu tlian in A. m arina. 



