The retractor muscles are thick and powerful, and attached along their length by
a muscular membrane to their corresponding longitudinal band. The whole muscular
system is very strongly developed, the longitudinal bands being remarkably thick and
robust, whilst the transverse series are numerous, and closely placed.
The Polian vesicles are long and thin, 10-15 in number, and of unequal length, the
longer ones being twice (or even more) the length of the shorter.
The alimentary canal is nearly three times the length of the body, and is bent twice
upon itself. Passing from the mouth it runs four fifths the length of the body; its
course is then reversed, and the canal proceeds as far as the anterior third of the body,
when it is again sharply bent backwards and passes to the anal extremity—the three
lengths formed by the convolutions being held in their places by mesenteries.
The mesenteries attached to the two lower portions are accompanied along the line
of their attachment to the body-wall by a longitudinal series of small pyriform bodies
of peculiar shape, attached to a common cord which passes nearly up to the oral extremity—
the “ infundibular g organs or “ Wimpertrichter.” Their form is represented in
Fig. 17; and it will be noted that they accord very nearly with those given by Sars of
C. pellucida, and in like manner with those of a Greenland specimen of C. Icevis, which
are figured for comparison.
The generative organs consist of two series of long and extensive dichotomosing
tubes connected together by a slender branch.
The largest example of this species has been recorded by Sars, and measured
100 millims. in length; generally, however, they range from 20 to 40 millims..
Premature Form.—In young stages the spots or sacculi which occur in the interradial
areas are smaller in number and proportionally larger in size than in the adult animal.
The calcareous wheels contained in the sacculi have both the spokes and the rim considerably
broader in the old than in the young form. Young individuals have also
fewer “ fingers ” on the tentacles, those of a small specimen 5 millims. in length having
only six digitations to each (Sars).
Variations.— Chirodota Icevis may unquestionably be regarded as a circumpolar
species; and the modifications which it presents are comparatively slight. We are
unable to consider the forms from Finmark and Lofoten, so carefully described by Sars
under the name of C. pellucida (Yahl), as other than the representatives of C. Icevis, the
Greenland type of Fabricius and Liitken, the modifications which led Sars to place
them as distinct species being frequently found much less pronounced, in both forms
mutually, than in the specimens he examined. Amongst the specimens of this species
procured by the ‘ Valorous ’ dredgings there are examples in which the form of the
wheels and of the tubular infundibular organs accord perhaps more nearly with Sars’s
figures of C. pellucida than with those which he gives for comparison of the same
structures from the specimen of C. Icevis which he had dissected. Upon both of these
points he placed great importance.
C. discolor, of Grube, from Behring’s Straits, although presenting greater divergence
than the above, seems indubitably to belong to the same type. The differences noted
in the form of the wheels and the structure of the infundibular organs, as well as the
greater length of the alimentary canal and the longer and more attenuated generative
L , are results which may not unnaturally be expected to arise when the distribution
of the forms compared is kept in mind.
Distribution.
a. Greenland: Godhavn, lat. 69? 14' N. (‘ Valorous ’ Exped. & Hayes's Exped.),
the most northern locality on record. . ,
b North o f American Continent: Labrador, 10 fins., sandy bottom M
Verrill) ; Grand Manan (Stimpson); Eastport, under stones at low water (Vemll).
1 Sitcha (under the name of C. discolor, Esehscholta). i I
c North o f European Continent: F i n m a r k a n d Lofoten, 1-2 fms., sand (&rs).
d. North o f Asiatic Continent: Ochotsk Seal (under the name of C. discolor,
Grube, Middendorff’s Exped.).
Description o f the Illustrations o f this'Species on Plate I.
Fig. 14. The animal, much contracted: natural size.
15. Generative tubes: magnified.
16. P o rtio n o f th e m o u th -rin g : magnified.
17'. The pyriform infundibular organs or “ Wimpertrichter magnified.
18. One of the wheel-like spicules: magnified.
19. One of the sacculi, to show the aggregation of the spicules: magnified.
Myeioteochus R inkii, Steenstrwp. Plate I, Figs. 20-24.
1851. Myriotroshm Rinkii, Steenstrup, Yid. Meddel. N. Porening i Kjobenhavn, 1851, p. 55, pi. iii.
jgs. 7-io. , , I im m
1852. Chiridota brevis, Huxley, Sutherland’s [ Journal of a Yoyage, Append, vol u. W |
1857. MyriMrochys Rinkii, Liitken, Yid. Meddel. N. Poremng 1 Kjobenhavn, 1857, p. 22.
1863. Myriotrochus Rinkii, Stimpson, Proc. Aoad. Nut. Soi. Philad. 1863, p. 142.
1867. Myriotroehus Rinkii, Selenka, Zeitsoh. f. iriss. Zool. Bd. xrik * 367.
1868 MyrwtroAm Rinkii, Semper, Beisen im Arckipel der PhiUppineu, Holothurien, p. $4, ■
1877. MyZtroshvs Rinkii (? pars), Theel, Nova Aota Beg. Sou, Soi. TTpsal. ser. 8, 1877, 40, xvn. p. 3.
Body cylindrical, and tapering only slightly towards the posterior extremity, in
some specimens the middle portion being somewhat swollen out, which causes the Holo-
thuroid to present a slightly arched profile. Anterior extremity very broad and
incapable of being retracted within the body, the habit of the animal being comparatively
short and thick, the length not more than four or five times the thickness. The
skin is smooth and whitish grey, and in some examples semitransparent, m which case
' the five longitudinal muscular bands as well as some of the internal organs axe visible
through the membrane. The surface of the body is overstrewn with large calcareous
wheel-shaped spicules of characteristic form, attached to the integument by means of a
short peduncle or prolongation of the skin, which is affixed to the central portion or
“ boss.” This, however, is not easy to be seen in all the spicules, as some are closely
oppressed to the body, in consequence no doubt of muscular contraction. The spicules,
as a rule, axe more numerous upon the dorsal than upon the ventral surface; in some