778 J. H. ARHWOETH. 



3. In the discussion of the systematic position of the 

 Otago specimens it is concluded that the form of the 

 otoliths is not sufficiently reliable to form a character by 

 which species may be discriminated. In A. marina the 

 otoliths are usually irregular, but two out of nine specimens 

 examined possess rounded otoliths. In these cases the 

 otoliths were at first irregular foreign bodies, but they 

 have been covered with layer upon layer of secreted sub- 

 stance, and now have a rounded outline. In each of these 

 two cases the tube which placed the otocyst in communica- 

 tion with the exterior has become either wholly or partially 

 blocked, either by apposition of its walls or by the secretion 

 into the lumen of a glandular substance which forms an 

 effectual plug. In the seven specimens of A. marina with 

 irregular otoliths the tubes are not closed in this way. It is 

 concluded that the presence of spherical or rounded otoliths 

 is associated with the closure of the tube, and it is pointed 

 out in support of this conclusion that the other species 

 (cristata, grubii, and ecaudata) in which spherical 

 otoliths are found have closed otocysts (pp. 7G1 — 7(33). 



4. The brain is well developed. The ganglion-cells of its 

 middle region are large (especially in the Otago specimens) 

 and send processes into the neuropile, where they branch 

 freely. 



5. Giant-fibres and segmentally arranged giant-cells are 

 present in the nerve-cord. They have the same structure as 

 in A. grubii. 



6. The otocysts of A. assimilis are distinguished by their 

 size. They are considerably larger than those of any other 

 species. Neuro-fibrillte may be traced from the nervous 

 sheath of the otocyst into and along the whole length of tho 

 sense cells of the otocystic epithelium. These cells and 

 fibrils are especially abundant near tho point of entrance of 

 the tube to the otocyst. 



7. There is a large nerve-supply to the skin and jjroboscis. 

 Neuro-fibrilloe may be seen in some of the cells of the general 

 body-surface and of the papilla^ of the proboscis. 



