of the Ophiuridae and the Echinidse. 439 



the pendulum descends, which may be compared in our larvae to 

 the framework of the mouth. The columns of the oral framework 

 also contain internally a calcareous column ; two of these calca- 

 reous columns are branches of the two belonging to the four main 

 columns, and pass off within the arched central body from those 

 of the former which support the tent. The other two calcareous 

 columns unite together at the back part of the dome at an angle, 

 from which a single branch ramifies in the dome. The skin, 

 which covers all the columns, the central body, and the expansion 

 at the mouth, is spotted with sulphur-yellow and brown spots. 

 The distribution of the ciliated organs is very peculiar. These 

 larvae are furnished with oblique tufts resembling epaulettes 

 which are situated upon those spots where the four supports of 

 the dome pass into it ; the tufts are also covered with very long 

 moving cilia ; a thick mass of sulphur-yellow pigment lies beneath 

 the tufts. Moreover these larvae are furnished with a row of cilia 

 upon all the columns and on the dome itself, as is the case with 

 the Pluteus. Two rows run upon each column ; these run into 

 one another at the extremity and superiorly at the dome from one 

 ray to the others. At the anterior margin of the dome, where 

 the latter is expanded like a tent, the row of cilia follows the 

 margin of this protection : not so at the sides j the arch of the row 

 of cilia here lies much higher than the margin of the dome, and 

 ascends almost as far as its summit. The columns also between 

 which the mouth and oesophagus are situated are covered by a 

 row of cilia, which passes from one ray to the other on the same 

 side, and in the centre runs beneath the mouth from one side to 

 the other. The mouth is surrounded by a distinct tuft of cilia. 

 It is triangular, and bounded inferiorly by an obUque, basin- 

 like projecting lip ; the two other or upper sides are inclined to 

 each other at an angle. In this direction the cavity of the mouth 

 is continued into the oesophagus, which leads to the blind sac of 

 the stomach. The latter receives the internal portion of the 

 arched central body, and is frequently bent in several places, so 

 that one portion of the blind sac is curved forwards. Both the 

 mouth and the oesophagus contract powerfully from time to time. 

 The interior of the cavity of the mouth, the oesophagus and the 

 stomach is ciliated. These larvae are about half a line long, and 

 live unattached in the water, their motions being entirely effected 

 by cilia. All the arms are immoveable ; the columns which lie 

 between the mouth and the oesophagus merely undergo a passive 

 motion from the powerful contractioi} of the mouth and oeso- 

 phagus. 



The first appearance of alteration is recognised in these larvae 

 by a discoid plate, which is produced in the months of August 

 and September on one of the narrow sides of the dome beneath 



