anterior and the posterior being absent—the result, according to Racovitza, of parasitism.
The two ventral nerve-cords are widely separated, with a ganglion in each segment, and
a transverse commissure. The alimentary canal has a muscular pharynx without dental
armature, with paired diverticula of the middle and hind gut, and a dorsal blind gut. A
vascular system is present, but both branchiæ and nephridia are absent. The sexes are
separate.
The genus Spinther was established by Dr. George Johnston in 1845 for an Annelid
(8. oniscoides) half an inch in length, and fully a quarter of an inch in breadth, which he had
received from W. Thompson of Belfast, who had dredged it in six to ten fathoms in the
neighbouring bay. It is remarkable that no undoubted example of this species has been
found in British waters since that date, though another species has once been procured in
the Minch. Dr. Johnston mentions its cream-yellow colour, the absence of distinct “ head,
tentacula, and tentacular cirri,” and gives the number of the dorsal lamellæ at thirty.
He correctly noticed the general form of-the “ feet,” the presence of the cirrus and other
features. He also distinguished the hooks and the various kinds of bristles, though his
figures were not drawn with that scientific accuracy—probably from deficient microscopic
power—which modern requirements demand. He grouped the genus under the Amphi-
nomidæ. Unfortunately the type-specimen1 is not in the British Museum, where Dr.
Johnston’s collection of Annelids is. The ciliated pits on the anterior portion of the
cephalic region are probably sensory (Racovitza).
Michael Sars five years later (1850) described his Oniscosoma arcticum, n. g. et sp.,
which he had dredged in Komagfjord, in thirty to fortyfathoms, on a sponge. This form
had twenty segments, a -tentacle and four eyes in the third segment. He gave an
account, of the dorsal lamellæ, the marginal expansions with the bifurcate bristles,
and the ventral division with the hooks. He linked it with Euphrosyne.
Edouard Grube next year (1851), in his ‘Eamilien der Anneliden,’ considered that
Spinther leaned to the Siphonostomæ or to the Amphinomea rather than to the Aphro-
ditidæ.
A few years later (1854) Dr. Stimpsoh formed the genus Cryptonota for a similar
Annelid,-giving most of the characters already known, and stating further that the
branchiæ resembled those of Euphrosyne, though he could not satisfactorily make them
out.
Grube (1860), in describing 8pvnther miniaceus, a new species, placed it near
Amphi/nome.
In A. de Quatrefages’ ‘Histoire des Annelés’ Johnston’s species is given at the end
of the Ohlorèmiens, under the genera and species of uncertain position, it being noted
that while Johnston considered it near the Aphroditidæ, Grube thought it approached the
Amphinomaceæ and Siphonostomæ, and that he (the author) was entirely of the latter
opinion, which he based on the structure of the feet, the presence of “ albuminous”
matter in them, and the nature of the hooks.
Claparède in a note2 states that the genera Spinther (Oniscosoma)and Cryptonota are
identical.
1 I am indebted to Prof. Jeffrey Bell for making a search.
2 ‘Arch. sc. Phys. et Nat./ t. xxii; ‘Bibl. Univ. et Rev. Scientif./ Apr., 1865.
Malmgren in his ‘ Annulata Polychseta ’ (1867) included Sars’s species under the
genus Spinther—as S-. arcticus, Sars.
In 1865 I found in the Minch, off North Uist, a form which was placed under 8.
oniscoides, Johnst., but which is clearly 8. miniaceus, Grube, or more correctly 8. arcticus,
Sars (non Wirën).
Hansen next- (1882) describes a form which he identified with 8. arcticus, Sars, from
the Norske Nordhavs-Expedition. The description and figures, however, as von Graff
says, agree better with 8. oniscoides, though the somewhat indifferent drawings of the
bristles leave some doubt.
In the account of the Annelids of the Vega Expedition (1888) Wir én described a
species which he calls 8. arcticus, but which materially differed from Sars’s form in size
and in structure.
The same year Levinsen, in his systematic account of the geographical distribution
of the northern Annelids, confused Sars’s species with Wirén’s, and made Hansen’s
(8. oniscoides) a new species.
Dräsche 1 further in 1885 gave an excellent anatomical description of 8. miniaceus,
Grube. He found this species chiefly on the surface of the sponge Tedania azihelans,
Lieberk., at Trieste. He pointed out the double nature of the dorsal membranes—of
the structure of which he gives good figures. Underneath the cuticle is the hypoderm,
which is thickened in certain regions. The muscular investment which occurs next is
more of less continuous as an outer longitudinal and an inner circular layer, but in his
figure (pi. ii, fig. 7) of the ventral region the reverse arrangement is shown. His
description and figures of the cephalic ganglia (brain) are good, as are also his remarks on
the eyes. He gives a clear account of the alimentary canal and of the dorsal blind gut,
which joins the intestine in front of the rectum. - His account of the circulatory system is
brief, since he had only examined the system in section—a dorsal vessel, a ventral trunk,
and transverse vessels in each segment being the chief features alluded to. He concludes
his paper with remarks on the body-cavity and its septa. Between each pair of septa are
the ganglia of the ventral cords and their commissure, the diverticula of the gut and the
transverse blood-vessels/ The rest of the cavity, in his specimens, was filled with the
reproductive products. In the male the region of the dorsal blood-vessel is specially
connected with thé development of the sperms, as Haswell and Selenka showed in the
Aphroditacea. He found no segmental organ (nephridium).
The most complete account of the genus, however, is that of L. von Graff (1887).
This author had an extensive series of specimens, and brought to bear on their structure
modern methods of investigation. After an historical introduction he gives the characters
of the genus and the three species known, viz. 8. oniscoides, Johnston, 8. miniaceus, Grube,
and 8: arcticus, Wirén. Thé adoption of the specific term arcticus for the latter, however,
seems to be open to some objections, since Sars’s name arcticus has some claim to priority
over Grube’s term miniaceus, and confusion may result from the application of the same
name to a different species, northern though it be. He shows that 8. miniaceus is the
smallest of the series, 8. oniscoides considerably larger (26 mm.), while 8. arcticus
1 Dräsche, R. von, ‘ Beiträge z. ferneren Anat. der Polychasta/ Wien, 1885, 14 pp., 2 pis.