EOSACETJS, LINCK (COMATULA EOSACEA OF LAMAECK). 
523 
the external layer of sarcode. The spicula are at first blunt irregular cylinders ; but 
shortly they fork at either end, and at length, by repeatedly dichotomizing and anasto- 
mosing, they form delicate plates of calcareous network. When definitely developed, 
these plates are ten in number, and they arrange themselves in two transverse rings of 
five each, within the wider anterior portion of the pseudembryo, the posterior row being 
slightly in advance of the pseudostome. These plates are at first round and expand 
regularly; the plates of the anterior row being arranged symmetrically above those 
of the posterior series (Plate XXIV. fig. 7.). They are imbedded in the substance of 
the sarcode, which for some time remains transparent within and without ; gradually, 
however, the space within the plates becomes turbid and opaque, and at length a rounded 
brownish granular mass fills up the lower portion of the cup formed by the calcareous 
trellis. A series, varying in number, of delicate calcareous rings may now be detected, 
forming a curved line passing backwards from beneath the centre of the lower ring of 
plates, behind and slightly to the left of the mouth of the pseudembryo ; and a large 
cribriform plate is rapidly developed close to the posterior extremity behind the anus 
(Plate XXIV. fig. 6). The rings are regular in their inner contour, but externally they 
are rough with minute branching spicula and excrescences. 
About twenty-four hours later the pseudembryo still retains its original form, and its 
rapidity of movement in the water is unimpaired. The anterior wider portion has 
become still more bulbous and enlarged, and a thick layer of firm transparent sarcode, 
thickly studded with columnar oil-cells, forms a dome-shaped arch over the anterior 
extremity. The sarcode external to the calcareous framework is extremely transparent, 
and the dark granular hemispherical brownish mass within the lower tier of plates is 
more clearly defined ; while above it and within the upper part of the space included 
within the plates, the outline of a second more transparent delicately granular hemi- 
sphere has become apparent. The two rows of plates are now irregularly square in 
outline, the plates of the lower series slightly contracted beneath, and those of the 
upper tier above; so that the ten plates forming the two rows, and now placed in close 
juxtaposition, form a delicate calcareous basket pentagonal in transverse section and 
slightly contracted above and below. A hollow sheaf of parallel calcareous rods, united 
together by short anastomosing lateral branches, is formed within each of the calcareous 
rings of the series passing backwards from the base of the calcareous cup. These 
sheaves are, as it were, hound in the centre by the calcareous rings, and the rods remain 
irregular and constantly increasing in length at either end of the sheaf, the irregular 
growing ends of the rods of one sheaf meeting and mixing with those of the sheaves 
next it. Thus we have formed what at first appears to be a continuous curved calca- 
reous rod; a slight amount of pressure, however, is sufficient to separate the joints from 
one another, and to show its true structure. The base of the sheaf of rods passing 
through the last ring of the series abuts against the centre of the upper surface of the 
circular cribriform plate, now rapidly increasing in size, and becoming more defined in 
contour, immediately behind the anus (Plate XXIV. figs. 8, 9, & 10). 
4b 2 
