EMBRYOLOGY AND ASEXUAL REPRODUCTION. 
Ech . 33 
yielding, as in the Ichthyocrinidai and in most recent Crinoids ; in this 
state, when the arms are opened, the ventral surface is depressed, when 
they are closed it bulges upwards. To afford better protection to the 
viscera the tegminal plates become more solid ; the tegmen, being thus 
less flexible, was fixed in its protruded state. The covering plates of the 
ambulacra had perhaps been closed from the beginning, but as, through 
the upswelling of the tegmen, they were now more exposed, further 
protection was needed. Consequently, they were lowered beneath the 
surface, and starting from the solid orals, interambulacral plates closed 
in over them. Certain of the covering plates, however, especially the 
axillary pieces, which perhaps could not be so easily covered by other 
plates, became much stouter, and were still exposed on the surface as 
solid radial dome plates. In any form highly developed along these lines, 
c.r/., Batocrinus , the food-grooves, water-vessels, and blood-vessels are 
sunk right beneath the tegmen, and are enclosed in a tube consisting of 
alternating ambulacral or covering plates above, and adambulacral or side 
plates below. The interambulacral plates of the tegmen send extensions 
into the interior of the calyx, which spread out and form what was 
formerly supposed to be a disc. In the Inadunaia fistulata tho dorsal 
cup never extended beyond the radials, and the tegmen was not developed 
to the same extent as in the Camemta. The orals did not, however, 
always persist in the simple stage in which they occur in the Larviformia, 
and in many cases they were entirely resorbed, and their places wero 
taken by large covering plates, of which the proximal ones joined in the 
centre. Ambulacral, and sometimes a small number of interambulacral, 
plates occur in the tegmen of the Cijatliocrinkloa ; besides there are four 
large plates, one in each interradius except the posterior, which rest against 
the radials, meet laterally beneath the ambulacra, and may be covered, 
to a varying extent, by small interambulacrals. A plate often similar to 
these four, lies between the ventral sac and the mouth ; this plate is 
profusely perforated in various Lower Carboniferous forms, and on 
either side of it lies a small narrow plate, which meets the adjacent 
large interradial plate beneath the ambulacrum. The authors believe 
that the perforated plate is an anambulacral, and the two narrow plates, 
and possibly the four larger ones, are subambulacrals. The anal plates 
are not regarded as homologous with the interradials, but are more 
supplementary still. [For further account and criticism, see F. A. B., in 
Geol. Mag., May, 1891.] 
III. — EMBRYOLOGY AND ASEXUAL 
REPRODUCTION. 
Brooks has studied Starfish larvae collected at Wood’s Holl, and finds 
that the water system is at first bilaterally symmetrical in every par- 
ticular, although the right water pore and tube disappear very early iu 
the life of the larva. Soon after tho formation of tho ciliated bands an 
1891. [vol. xxvm.] F 3 
