502 F. W. GAMBLE AND J. H. ASHWORTH. 



This entire absence of any trace of the otocysts in A. 

 Claparedii is very remarkable^ since in other species of the 

 genus these sensory organs are perfectly constant^ and, so 

 far as is known at present, they are unrepresented in any 

 of the families (Maldanidse, Opheliidse, Scalibregmidae, 

 Capitellidse) with which Arenicola shows a more or less 

 close degree of resemblance according to the organs under 

 consideration. 



In A. marina the structure of the otocyst and the nature 

 of the otoliths are both well known. In describing the 

 oesophageal connectives we pointed out that the nerve to the 

 otocyst arises from them, and is strongly ganglionated. We 

 have now only to add that in post-larvce 4*5 mm, long, taken 

 while swimming freely in their gelatinous tubes, the otocysts 

 contain minute quartz-grains covered by a delicate chitinoid 

 film. This seems to point to the conclusion that these young 

 stages are not strictly pelagic, but that they sink to the 

 ground for a longer or shorter period of time, and probably 

 are disturbed by the incoming tide and so brought near the 

 surface, for it was at high tide that our specimens were taken 

 at Lytham by Mr. Ascroffc. Wilson's observations on the 

 habits of very young A. cristata show that the true early 

 larval stage is a free-swimmer, but that later on the animals 

 sink to the bottom and creep about while retaining the power 

 of swimming. 



Of the three remaining species the otocysts of only one 

 specimen of A. cristata have been examined by Ehlers, 

 with whose account we are in full accord. There is only a 

 single otolith, chitinoid in nature, which appears to increase in 

 size with the age of the Arenicola. A small specimen of 

 this species, 47*5 mm. long, had an otolith of lenticular shape, 

 and measuring "07 mm. in length, "028 mm. in width, and 

 •056 mm. in thickness ; while in another example from 

 Naples, 300 mm. long, the cavity of each otocyst measured 

 •018 mm. in diameter, and the almost spherical otolith 'OlS 

 by "012 mm. We have fully confirmed Ehlers' statement 

 that in this species the otocyst is closed ; in fact, the 



