236 bulletin: museum of compaeatiye zoology. 



the radial and circular muscles might find sufficient occupation in pro- 

 ducing the movements necessary for the intalie and discharge of the 

 ■water essential to respiration and nutrition. 



The rootlets of 0. herdmania are not merely processes of the test, as 

 Metcalf, 1900, speaks of those of 0. patagoniensis as being. Each is a tube 

 whose wall is of test, and within which is a delicate axial muscle band 

 consisting of two or three fibres. Here and there along this band nuclei 

 are to be seen. In general structure these rootlets resemble more closely 

 those of Rhizomohjula Ritter, 1901, than of any other ascidian with 

 which I am acquainted. They are, however, much more delicate here 

 than in that molgulid. They do not branch here as there, each arising 

 direct from the body of the animal. They are not more than three or 

 four mm. long. It is usual for ascidian root-hairs of this sort to cling with 

 great tenacity to the mud and sand in which they are embedded, so 

 that they are freed from foreign particles with difficulty. It is, con- 

 sequently, surprising to find them quite clean in Odacnemus. This 

 fact suggests that the animal is not very firmly anchored to the 

 bottom. But while the individual rootlets were entirely devoid of 

 foreign particles clinging to them, entangled among them were many 

 slender, sometimes branched, brown tubes. These seem to belong to 

 the foraniiuiferous genus, Rhizammina of Brady, and to be close of kin 

 to R. dlgaeformis. In addition to these, numerously present over the 

 entire adhesive disc of all the specimens, several fragments of a hexacti- 

 nellid sponge were entangled among the rootlets of one individual.' 

 Finally, a few Globigerinae were associated with the rhizopod tubes. 



Moseley mentions that the " border of the base [i. e. of the ventral 

 surface of the oral disc] is thickened into a slightly prominent, rounded 

 ridge, running round the periphery of the entire basal area." This 

 author's schematic section of the animal, shown in a text figure, indicates 

 this prominence at h. This ridge is decidedly more than "slightly 

 prominent " in the " Albatross " specimens. In life it must amount to a 



with the tow-net in 150 fathoms. This was during his Expedition to the Tropical 

 Pacific in 1899-1900, tlie station at wliich the capture was made being in lat. 

 4° 35' N., and long. 136° 54' W. Mr. Agassiz also tells me by letter that Octacne- 

 mus was taken at two or three other localities between 300 fathoms and the 

 surface. With this information, and with what seems to me the certainty that the 

 animal rests on the bottom at times, the question of the life habits of the species 

 becomes of increased interest. Note by A. Agassiz. — It is very probable that 

 the fragments of the bottom sometimes found in the rootlets of Octacnemus have 

 become entangled in them while in the trawl on its way to the surface after the 

 specimens were obtained in bathyraetrical belts less than 300 fathoms. 



