and Shells of Massachusetts Bay. 11 
pable of any locomotion except on the bottom, remark- 
ing, * Les Eolides ne sauraient nager, et rampent seule- 
ment dans les fonds des mers." This however is incorrect, 
as I have frequently observed them swimming along with 
considerable speed, in an inverted position, near the 
Surface; and found them almost invariably creeping 
about on the alge &c., but a short distance below it. 
Their movements, generally, are much more rapid than 
. those of the "T'ritoniz. 
In the description and figure of E. Cuviéri given by 
De Blainville, * Man. de Mal. &c." p. 486, pl. 46, bis, 
fig. 8, 8°, the genital and anal orifices are placed nearly 
above each other; a position which is occupied by nei- 
ther of them, in the species inhabiting our waters. "The 
difference of arrangement is so great indeed, in this 
respect, as almost to warrant our considering the latter 
as belonging to a distinct genus. 
The branchiz, usually so termed, are capable of erec- 
tion and depression, simultaneously or individually, in a 
manner similar to the spines of the Echinus, and are 
constantly so in motion. Although I may be reproached 
with temerity, for venturing to dissent from the generally 
received opinion upon the subject, I would here express 
strong doubts, whether what are commonly denominated 
the branchiz in these animals, do actually perform the 
office of respiratory organs, at least unassistedly. These 
doubts have arisen in my mind, in consequence of ob- 
serving the facility with which the cirri are detached 
from the body, either when the animal is raised by them, 
Or upon contact, by no means violent, with foreign 
bodies. I have repeatedly known these appendages to 
be almost entirely removed, and yet the animal live for 
several days. This was the case with the specimen of 
