440 Prof. Miiller on the Larval State and the Metamorphosis 



the spotted skin of the latter, and which is inchned at an acute 

 angle towards the summit of the dome. In our comparison of 

 the framework with a pendulum it forms as it were the dial-plate, 

 but the position of the dial-plate would be heterologous to that 

 of the pendulum, and it would be situated at the side of the 

 clock-case. This disc is thus heterologous in position with 

 the mouth of the larva. The round disc, which is now but 

 slightly convex, becomes itself again spotted with yellowish spots. 

 It is divided by a five-leaved figure into five valve-like divisions, 

 which are almost in contact in the centre ; at the circumference 

 there are intermediate segments between them. Each valvular 

 division has two outlines which are widely separated from each 

 other. Opposite this disc, which forms the earliest appearance 

 of the Echinus, there appear upon the dome on each side pedi- 

 cellarife, which are furnished with three arms such as are peculiar 

 to the Echini', for the pedicellarise of the Asteria have two arms. 

 The pedicellarise lie close to the dome ; at this period they also 

 exhibit spontaneous motion, the arms of the pincers opening and 

 shutting. The larva has usually only four pedicellarise, tw^o on 

 each side, situated near to each other. 



During the growth of the disc within the dome, new seg- 

 ments appear at its marginal portions which inclose the five cen- 

 tral plates : externally between the five plates there appear five 

 circular figures with double outlines ; these are the foundations 

 for the tentacles or feet ; for the young Echinoderm which is at 

 this period in the progress of formation possesses the peculiarity, 

 that at first it is furnished with only five regular, symmetrically 

 distributed, large, odd feet, which rise from the apertures of the 

 disc in the form of minute cseca with double outlines. The 

 other peripheral segments, which cannot be confounded with the 

 plates of the shell of the adult Echinus, soon shoot up into cylin- 

 drical elevations, which are converted into spines. When the 

 young Echinus is so far developed as to form a slightly convex 

 disc furnished with spines and five tentacles or soft feet, both 

 the feet and the spines project far beyond the surface of the 

 dome of the larva, the feet move in all directions in a groping 

 manner, and are now in a condition to adhere to objects. The 

 spines are also moveable at the will of the animal. The mouth 

 of the larva still remains in its former position, and like the oeso- 

 phagus is in full action. The feet are annulated, and like the 

 spines, sparingly spotted w^ith a yellow and brown pigment. Each 

 of the five feet is furnished at its extremity with a disc, in the 

 centre of which there is a tubercle, just as in the feet of the adult 

 Echinus in their extended state, and as figured by Monro from 

 life. Within the disc we find a polygonal simple calcareous 

 rim. The minute feet are hollow internally, but at the extremity 



