222 PROCEEDINGS OF SOCIETIES, 
these spicula rapidly expand into ten plates, which at length form 
a trellis enclosing a dodecahedral space, open above and below, 
within the anterior portion of the zooid. Simultaneously with the 
appearance of these plates, a series of from seven to ten calcareous 
rings form a chain passing from the base of the posterior row of 
plates backwards, curving slightly to the left of the larval mouth, 
and ending by abutting against the centre of a large cribriform 
plate, which is rapidly developed close to the posterior extremity 
of the larva. Delicate sheaves of anastomosing calcareous trabeculee 
shortly arise within these rings, and the series declares itself as the 
jointed stem of the pentacrinoid stage, the basal and first inter- 
radial plates of the calyx being represented by the already formed 
casket of calcareous network. The skeleton of the Crinoid is thus 
completely mapped out within the body of the larva, while the 
latter still retains its independent form and special organs. 
Within the plates of the calyx of the nascent Crinoid two hemi- 
spherical or reniform masses may now be detected—one superior, of 
a yellowish, subsequently of a chocolate colour; the other inferior, 
colourless and transparent. The lower hemisphere indicates the 
permanent alimentary canal of the Crinoid, with its glandular 
follicle; the upper mass originates the central ring of the ambu- 
lacral system, with its ceeca passing to the arms. ‘The body of the 
Crinoid is, however, at this stage entirely closed in by a dome of 
sarcode, forming the anterior extremity of the larva. After swim- 
ming about freely for a time, averaging from eight hours to a week, 
and increasing rapidly in size till it has attained a length of from 
1 to 2 mm., the larva becomes sluggish, and its form is distorted 
by the growing Crinoid. The mouth and alimentary canal of the 
larva disappear, and the external sarcode-layer subsides round the 
calcareous framework of the included embryo, forming for it a 
transparent perisom. The stem now lengthens by additions of 
trabeculee to the ends of the joints. The posterior extremity 
dilates into a dise of attachment. The anterior extremity becomes 
expanded, then slightly cupped; the lip of the cup is divided into 
five crescentic lobes, corresponding to the plates of the upper ring ; 
and finally five delicate tubes, ceeca from the ambulacral circular 
canal, are protruded from the centre of the cup, the rudiments of 
the arms of the Pentacrinoid. At some stage during the progress 
of these later changes the embryo adheres, and at length becomes 
firmly cemented to some permanent point of attachment. 
The author states his yiews as to the morphological and physio- 
logical relations of the larval zooid. He believes that all the pecu- 
liar independently organized zooids developed from the whole or 
from a part of the segmented yolk in the Echinoderms, and which 
form no stage in the development of the perfect form of the species, 
must be regarded as assimilative extensions of sarcode, analogous 
in function to the embryonic absorbent appendages in the higher 
animals. T'or such an organism the term ‘‘ pseudembryo”’ is pro- 
posed. In the Echinoderm subkingdom, although constructed 
apparently upon a common plan, these pseudembryos present con- 
