216 LECTURE X. 



before the anus, completely encircling the body obliquely, and is con- 

 tinued upon the processes, all of which are developed in one direction, 

 in which they are divergent, and the creature is more plainly bilateral ; 

 the processes are also longer, and have no relation to fixation. The 

 body is conical and pointed behind, and branches into eight processes 

 in front ; these contain calcareous rods and spiculae, which also occur, 

 interlacing, on the upper part of the body ; the lateral processes are 

 the longest, and each process is provided with two ciliated borders, 

 which are prolongations or continuations of the encircling fringe. 

 The obtuse points of the body, and the ends of the processes, are 

 orange-coloured : the other parts are colourless and transparent. 

 These Plutei occur in great numbers in August and September, when 

 they are from one to two lines long : they swim freely, with the pro- 

 cesses turned forwards. One part of their truncated side is prolonged 

 into a single flat and wide process, which carries the mouth and 

 gullet : on the side of the hemispheric portion opposite to this is the 

 circular anus. The mouth and stomach are ciliated. A little con- 

 tractile movement of mouth and pharynx may be noticed ; but the 

 streams of nutriment are seen, by means of indigo, to be directed by 

 ciliary action towards the mouth. Two small ganglions are situated 

 below the mouth, from which nerve-filaments diverge. These larvae 

 are not luminous by night. 



The first indication of the production of an Ophiura, within the 

 Pluteus, is the appearance at the sides of the stomach and pharynx, 

 or the granular germ-mass, of certain caecal winding tubes, with a 

 double contour: they soon surround the so-called stomach like a circle ; 

 they next project from the surface, like tubercles ; then the whole 

 takes on the form of a disc, with five short processes. The em- 

 bryonal ciliated arras, or rods, take no share in the formation of this 

 disc. Calcareous spiculae begin to take a new arrangement on the 

 nascent disc and arms. The mouth of the Ophiura is a new forma- 

 tion ; it is at first round, and quite distinct from that of the Pluteus, 

 which disappears. Before the processes of the Pluteus disappear, 

 the tentacula of the arms of the Ophiura are developed. Short 

 processes, or pinnae, next shoot out on each side the base of the 

 elongating rays, or arms, and these processes move violently. The 

 remnant, or case, of the ciliograde Pluteus is absorbed or cast off, 

 and the young Ophiura is plainly manifested. The transparent gela- 

 tinous larval animal, from its general resemblance to the Bero'idce, 

 might be classed with the ciliograde acalephae, but for the appearance 

 of certain opaque lines of calcareous matter. 



In regard to the next order, the Echinoidea, the observations of 

 Prof. MUller are more full and remarkable. His attention was 



