reason of extreme crowding. Owing to the densely tessellated and compact nature of
the integument, the sucker-feet are incapable of being perfectly retracted; and this
circumstance, together with the size and general habit of the animal, affords a striking
superficial feature, which readily characterizes the species amongst its Arctic congeners.
The cuticle, although thin, is very strong, being indurated with calcareous plates,
of which two distinct layers are present; in each of these the plates are quite different
both in size and form, and are so closely packed as to imbricate upon one another,
whilst the whole Holothuroid is rough and scabrous to the touch, in consequence of
a small spiculate elevation which rises from the centre of each of the plates that form
the superficial layer.
The tentacles are ten in number, two being much smaller than the rest. They are
of delicate habit, and redivided into many branches, which are fine and thin.
The mouth-ring is elongate, and resembles in a marked degree the form found in
Thyone. I t is composed of ten plates, each of which is made up of two elementary
pieces, as may be well seen in the mouth-apparatus of a young specimen (Plate g§ Fig. 4).
The radial elements are produced upward into a fine wedge-shaped peak, and downward
into two long, thin prolongations, which extend to the base of the apparatus, the
cleft formed between them being wide and well arched above. The alternating inter-
radial elements are somewhat wedge-shaped, equal in size to the upper portion of the
radial processes, and extend upward to. the same height as these. The angle of
the plates, which abuts against the neighbouring radial member, is somewhat truncate,
and the suture between the two primary pieces slightly hollowed out in the
middle.
The Polian vesicle of a young individual is represented in Fig. 4, in which
it is seen as a very distended sac, emanating midway upon a fine short tube.
According to Dr. Liitken (l. c.) the respiratory organs in the adult animal cleave
immediately into four rays, .one small and one larger on each side. They are but feebly
branched; and although becoming generally thicker towards their extremities, it is only
here and there that any thing like a vesicle can be detected.
Respecting the anatomy of the alimentary canal, it may be noted that the oesophagus
is moderately developed, with its outer wall villate or densely covered with minute
papillae, and that the intestine is large and much convoluted.
The muscular system is somewhat small for a Cucvmaria. The m. longitudinales
are thin and very narrow, and the m. transversales similarly slight. The m. retractores,
however, are strong and by far the most powerful bands of muscle in the animal; they
are attached to the central part of the wedge-shaped upper portion of the radial member
of the calcareous ring, and join the longitudinal band of muscles midway between
the extremities. "When the mouth-apparatus is retracted and these muscles are relieved
from tension, they appear very broad in comparison with the other bands, and are,
besides, much swollen out in their middle portion. The m. extensores are very fine
indeed and double, and are affixed to the radial pieces of the ling a little above the
attachment of the retractor muscles.
The reproductive organs consist of simple tubes. A figure is given of their condition
in an early stage of growth (Plate I, Fig. S)| J<: ■’* ‘
The calcareous plates and spicules which indurate the integument are highly characteristic.
As previously stated, they are so closely placed as to imbricate upon one
another; and it is consequently very difficult to determine the form of individual pieces
until separated by treatment in baustic potash. The plateg which form th|gmtermost
layer, vary in shape from roundish to oblong, and even irregularly stellate forms, their
greatest diameter ranging from 0-28: to 0-35 millim. (Liitken). They are perforated with
closely-placed holes, whose distance apart is less than their diameter, no plan being
discernible in their arrangement,: From the centre of each rises a suhconical elevation,
made, up of fine calcareous rods, about one third as high as the diameter of the plate,
and which terminates with two or three spikelets. It is to these spicular plates that
the rough texture of the skin is due, and the granular appearance it presents when
examined with a hand-magnifier of low power.
Underlying the plates just described is another layer of oblong and much narrower
plates, also closely packed together and overlapping, and which are present in greater ,
number over a given area in consequence of their smaller size. These pieces are generally
punctured with two (or - sometimes three) rows of holes, which become smaller in
diameter towards the extremities of the plate.
The skin of the sucker-feet is comparatively as densely plated as that of the body,
the spicules at the base beings similar in character to those above described, but smaller
in size; towards the,, extremity, however, they become much narrower, bear fewer holes;
and are somewhat more curved, whilst mixed up with them may be found a number
of quite rudimentary plates. When the great number of these scales and the method
of their arrangement are borne in mind, the reason of the suckers being incapable of
retraction becomes at once self-evident, as well as that of the small size of the internal
ampulla;, which follows as a correlative result. The calcareous disk at the extremity of
the sucker is well developed and very characteristic. I t is a delicately fine circular
network, having the immediate centre occupied with a number of small round holes, the
rest of the piece being characterized by large subhexagonal apertures, which diminish
in size as they approach the margin.
Respecting the affinities of G. calcigera, it may be said that although the form bears
undoubted resemblance to Gucumaria Hyndmanni, Thomson, this is in external appearance
only, as has been already pointed out by Diiben and Koren*; whilst Liitkenf, in
his description of G. Kormii, specified in detail the differences which exist between the
two species. As a fact, the calcareous plates are altogether different;—in G. Hyndmanni
being alike and. constant in form, whilst in C. Korenii (— C. calcigera) there are not
only two layers of quite distinct kinds, but the plates themselves vary very considerably.
The plates also of the sucker-feet are broader, perforated with more holes, and are less
regular and less uniform than in G. Hyndmanni; and, lastly, the fully-developed disk at
the extremity of the sucker is characteristic of the present species.
* Kongl. Yetensk. Akad. Handl. &r 1844, p. 299.
f Yidenskabelige Meddelelser f. d. Naturh. Forening i Kjobenkavn 1857 p. 6.