40 1 Ucli. 
ECH1NODERMATA. 
“ brachiolar appendages” of Asterias violacea , and corresponds to the 
“larval organ ” of Asterias jlaccida and Asterina gibbosa ; in other words, 
to the preoral lobes of Asterid larva). Hence, the “ umbilical cord ” of 
these larvae would correspond to the stom of Crinokh. In its anatomical 
structure the umbilical cord is a diverticulum of the body-wall. The 
mode of attachment appears to be similar in Diplasterias lutheni , E. P., and 
D. steineri , Studer. Pterasler higoufi and incisus also incubate their young. 
According to Russo (2), the hydrocoele of Amphiura squama ta arises 
from one of the mesoblastic sacs, and becomes divided into five lobes. 
Each lobe becomes divided by two lateral furrows, first into four por- 
tions, which are the future buccal tentacles and the first brachial tentacles. 
After them a fifth lobe arises, the future radial canal. The water vascular 
ring arises by elongation of the parts of the hydrocoele vesicle between 
the five primitive lobes. The Polian vesicles arise as swellings of the 
interradial tracts. The stone canal commences by an aperture placed in 
the lower part of the hydrocoele, later becoming a canal placed in the 
proximity of the five last tentacles. The embryonal calcareous skeleton 
appears as two spicules, homologous with those of other Ophiuvkls. The 
permanent ventral skeleton commences with small corpuscles placed closo 
to each tentacle. 
Russo (3) finds that in Amphiura squamata the segmentation results in 
a blastula composed of elongated cells, each of which is of an intense red 
colour in the central part, while the peripheral portion is clear and con- 
tains the nucleus. The red colour is derived from the yolk elements of 
the egg. The endoderm arises by delamination, each cell of the blastula 
dividing in two, the coloured portion becoming endoderm, the clear 
portion ectoderm. This multipolar delaminatiou is in connection with 
the development of the Amphiura in the maternal body, and in contrast 
with Echinoderms which develope free in the water, where the develop- 
ment of the endoderm is unipolar. 
At this stage a degeneration commences, at a certain pole, first of the 
ectoderm and then of the endoderm, and by the resulting perforation the 
proctodasum and archenteron are formed. The mesoderm then arises 
from the endoderm by delaminatioii, forming two groups of cells on each 
side of the archenteron. The cells apply themselves to the two primary 
layers, and thus enclose a space, the body cavity. 
Russo (5) describes the segmentation and formation of the germ layers, 
archenteron, enterocoele, stomodaeum, proctodaeum, and nervous system, 
in Amphiura squamata. The first two blastomeres are of unequal size ; 
the larger one divides first, so that there is a stage of three nearly equal 
blastomeres, which is followed by a stage with four. There is a morula, 
followed by a blastula. The nervous system appears when the stomo- 
daeum and proctodaeum are formed, and is represented at its origin by 
four yellowish cells, with prolongations by which they are attached to the 
ectoderm, and to the stomodaeum at the side of which they are situated. 
They are probably derived from the ectoderm by delamination. [Cf. 
Russo (2, 3).] 
