754 J. n. AsnwoRTH. 



present in the coaguluiii to spherical, oval, or elongate masses 

 10 n in diameter, which are either free or adliering to the 

 surface of one of the otoliths. Their appearance suggests 

 that thej are composed of a substance similar to that of 

 which the otoliths are formed, although the latter are usually 

 much more lightly stained (fig. 13). 



'I'he nuchal organ of A. assimilis resembles that of A. 

 marina in its main features. The epithelium of the organ is 

 composed of exceedingly slender columnar cells ; some of 

 these — the sense cells — are 70 /u to 80 /x long, and only about 

 2 n Avide, and have deeply staining nuclei. The intervening 

 supporting cells are a little stouter, and their nuclei stain less 

 deeply. Many of these cells are ciliated, and some are 

 glandular. Beneath the epithelium there is a la3'er of nerve 

 elements in connection with the posterior brain-lobes. From 

 this layer neuro-fibrillas may be traced into and through the 

 entire length of many of the sensory cells. 



Similar fibrils may be seen in some of the epidermal cells 

 of the general body surface, and of the papillae of the 

 proboscis. 



III. Specimens of Arenicoia from New Zealand. 



Three of these were collected in Otago Harbour, and are 

 respectively 13G, 126, and 90 mm. long. Another specimen 

 from the Macquarie Islands is 217 mm. long. The Otago 

 specimens are of a light brown colour, the two larger ones 

 being darker in the anterior gill region, and the Macquarie 

 specimen is dark brown throughout its length. 



External Characters. — The prostomiuin (fig. 20), the 

 nuchal organ, and the metastomial grooves agree in form and 

 relations with those of A. assimilis. There are nineteen 

 chactigerous segments, of which the last thirteen usually bear 

 gills. The first gill is thus situated on the seventh segment, 

 as in A. marina, A. claparcdii, and A. cristata. The 

 gills of the two larger Otago specimens are all fully developed, 

 but in the smallest specimen the last right gill is smaller 



