138 BULLETIN OF THE 
the characters in synoptic form. The original description (Verrill, ’79) 
has been followed as closely as was compatible with the changes necessi- 
tated by the discovery of the female, and by a more perfect acquaintance 
with the anatomy of the male. 
Nectonema, Verrill, char. emend. — Body long, slender, nearly round. 
Cuticula finely ringed, on the median lines often deeply infolded and 
bearing on each line two rows of hair-like bristles. Bristles hollow, 
superficial and unconnected with each other. Head without appen- 
dages, obtusely rounded or bluntly conical with a shallow dorsiventral 
furrow on its anterior aspect. Mouth-opening in the centre of this fur- 
row, minute. In the male the tail is curved ventrad, and terminates in 
a small conical intromittent organ. Female smaller, the posterior end 
slightly enlarged, abruptly truncate, with terminal vaginal (?) opening. 
Alimentary tract rudimentary and anus wanting in both sexes, 
Nectonema agile, type species. — A long, slender, and exceedingly 
active round worm, resembling in form and motions a Gordius, found 
swimming at the surface of the sea with a rapid undulatory motion. 
Integument firm, opaque, smooth, except for many minute circular ridges 
interrupted at the median lines, which are themselves often thrown 
into larger, deeper folds, locally very prominent. Body in life round, of 
nearly uniform size throughout, tapering slightly close to the head, and 
somewhat more towards the posterior end in the male. Each! median 
line is distinguished by two narrow longitudinal bands of minute dots 
between which stand two longitudinal rows of hair-like bristles. The 
worm undergoes torsion in the anterior third of the body, so that the 
median lines appear lateral in the posterior two thirds of the body. The 
double row of bristles extends from a point 1 or 1.5 mm. behind the apex 
of the head to about the same distance from the posterior extremity of 
the body. The bristles are 0.3 mm. in length, opposite to each other, 
hollow, unconnected by any web, entirely superficial, and hence easily 
detached and often injured or lost over considerable stretches of the 
body. The head is marked anteriorly by the presence of a shallow 
median dorsiventral furrow, on each lateral edge of which are one, some- 
times two, low rounded papille. The anterior portion of the body is 
semi-transparent, externally not separated by any constriction from the 
rest of the body ; but internally an anterior chamber is divided from the 
general body cavity by a partition which is concave anteriorly. The an- 
terior chamber is traversed by the oesophagus, and contains ventrally the 
brain, while the dorsal space is filled by four large conical cells which 
send processes down into the nervous matter of the brain, The œsopha- 
