184 ECHINODEEMATA. 



make their appearance, sprouting, as it were, from the anterior part 

 of the body, and ultimately appearing as four club-shaped processes 

 (fig. 91, 10, 11, 12, 13, a a) surrounding a fifth prominent protuberance, 

 6, whereby the little creature fixes itself to the sides of the incubatory 

 cavity. The body of the little Star-fish now becomes gradually flat- 

 tened into a minute circular disk, upon one surface of which hence at 

 once distinguishable as the ventral the rudiments of tentacula begin 

 to be apparent, under the form of minute globular protuberances, dis- 

 posed in ten concentric rows (fig. 91, 14, 15, c e}. 



(483.) If in this condition the little being is detached from the spot 

 where it has fixed itself, it is still able to swim about in the surround- 

 ing water by means of its ciliated surface, always keeping the organs 

 of attachment directed forwards; but if left undisturbed, it remains 

 perfectly still and motionless, presenting what M. Sars denominates the 

 crinoid state of development. At this stage, the body of the young 

 Star-fish may still be said to be bilateral ; for in all its movements 

 the organs of attachment are directed forwards, and both sides of the 

 body correspond exactly to each other (fig. 91, 12). But by degrees this 

 bilateral condition is converted into the radiated form that charac- 

 terizes the third, or perfect condition of the Asterias ; the body gradu- 

 ally assumes a pentagonal outline, from the angles of which short blunt 

 rays begin to project (fig. 91, 16) ; and the tentacula, now presenting 

 the form of retractile cylinders, and completely furnished with their 

 terminal suckers, become efficient instruments of locomotion. The red 

 spots, regarded by Ehrenberg as the eyes, are visible at the extremities 

 of the nascent rays ; the mouth shows itself in the centre of the ven- 

 tral aspect of the body ; and numerous spines make their appearance. 

 Lastly, the apparatus for attachment begins to diminish in size, and 

 soon completely disappears, so that the young Asterias, having attained 

 its perfect form, is ready to enter upon the duties of its station. 



(484.) According to the observations of Agassiz, the eggs of the Star- 

 fish, after they are laid, are taken up by the parent animal and kept 

 between its tubes below the mouth. The Star-fish bends itself around 

 them, surrounds the eggs with its suckers, and moves about with them. 

 When the eggs have been removed to some distance from the animal, 

 it has been observed to go towards them, take them up again, and move 

 off with them, showing that these creatures, so low in structure and 

 apparently deprived of all instinct, really watch over their young. As 

 the growth of the embryo commences, the external crust of the germ 

 becomes more transparent, consisting of somewhat looser and larger 

 granules, and the internal mass assumes a darker colour, so that two 

 layers become distinct, between which a third is developed. On one 

 side of the germ a protuberance now becomes visible, and the promi- 

 nent portion separates more and more from the spherical mass, assuming 

 by degrees the form of a peduncle. At this period there is not any 



