GENERAL MORPHOLOGY OP THE GROUP. 
Ech, 4 
are delicate fibrils, with* pale bi-polar cells, which are scattered and not 
collected into ganglia. 
Lyman (22) finds that a number of membranous pouches are con- 
nected with the stomach of the Astrophytidm, and that the space between 
the ten radiating compartments and the “stomach-sphincter” differs only 
from the perihaemal canal of the Ophiurida in not being closed. The 
ova would seem to be impregnated in the body-cavity. Differences 
in various forms and approachments to the Ophiurida are pointed 
out. 
A study of Ainphiura squamata has convinced Ludwig (21) of the 
truth of the doctrine that the arm-ossicles of the Ophiurida are originally 
double ; the first rudiment consists of two calcareous pieces symmetri- 
cally placed on either side of the middle line of the arm ; of the three 
rays of each triangular piece, one is directed ab-orally, and two ad-orally ; 
the first increases considerably in length, and the two ad-oral pieces 
gradually become connected. Lateral and mesial growth only gradually 
leads to complete fusion, and, till a late stage, there is a space with con- 
cave sides in the middle of the ossicle. The radial water-vessel is not, at 
first, covered over by the ossicle. The lateral plates of the arm of an 
Ophiurid may certainly be regarded as homologous with the ad-ambu- 
lacral plates of the arm of a star-fish ; the ventral and dorsal plates are 
primarily unpaired. There is a striking similarity in the position of the 
primary madreporic pore of Amphiura and of the larval Antedon. 
Geddes & Beddard (17) find that in the ophiocephalous pedicellarise 
the muscles uniting the head to the stem mostly terminate in a series of 
loops outside the calcareous parts ; the muscles only present strioe when 
the fibres are constricted. 
Perrier (24) notes the characters of the podicollaria} of deep-sea 
Asteroidea\ Archaster mirahilis sometimes has a “comb” of spines; 
some Luidim have four branches to their pedicell arise. 
Foettinger (16) describes in detail the minute structure of the pedicel- 
lariae of Sphmrechinus granulosus, where the head and the glands are 
equally developed ; in Echinometra the head, and in Diadema the glands, 
are better developed. In Mespilia globulus these organs are excessively 
small and very numerous ; Strongglocentrotus lividus and S. drohachi- 
cnsis have a stalk which is very similar to that of the ophiocephalous 
and tridactyle pedicellarim. 
The viviparous Chirodota described by Ludwig (19) had sixteen young 
lying freely in its coelom ; the calcareous wheels have at first the form of 
a six-rayed star, the circumference of the wheel being formed later on 
by the union of the adjacent processes. The stone-canal presents an 
intermediate character betw^een those in which all connection is lost, and 
those in which connection is retained with the exterior. Indications of 
auditory vesicles were detected. 
On the Morphology of the Palmozoic Crinoids, see Carpenter & , 
Etheridge, Ann. N. H. (5) vii. pp. 281-298; and consult the second 
part of the important Revision of the Palceocrinoidea, by Wachsmuth & 
Springer, P. Ac. Philad. 1881, pp. 177-414, pis. xvii.-xjix. The value of 
a study of fossil f oi ms is illustrated by the essay of Neumayr (23). 
1881. [voL. XVIII.] H 2 
