388 Mr. T. H. Stewart on the young state of Opbiocoraa rosula. 



The disk in this young state is more pentagonal than in the 

 adult animal. It is of a deep yellowish-brown or purple colour, 

 and it was this part that rendered the starfish evident on the 

 sponges. 



The entire starfish was very transparent, so that the move- 

 ments of the stomach and parts within could be distinctly seen 

 under an inch power (100 diam.). 



The disk was spinous, but had the spines more irregularly 

 arranged than in the full-grown starfish. The forms of the spines 

 are those depicted in PL XV. fig. 4. They were most distinctly 

 seen on the borders of the disk, between the rays, and all of 

 them had a like typical form, though some differed from others 

 on the same starfish in slight particulars, as the length of the 

 stalk bearing three spinules or secondary spines. 



The base of these spines is a flattened disk, and somewhat 

 circular in form ; immediately above the base is a contraction, 

 and it then shows a perforated structure ; the holes producing 

 these perforations are regular and arranged in the central line. 

 The length of the stalk is rather less than half the length of the 

 whole spine. The spine then separates into three prongs or 

 spinules, which are rather more than half the length of the 

 whole spine. 



These spinules in some spread out wider apart than in others, 

 and in one they approached each other again at the tip. All the 

 spines of the disk are of this form, and they retain the same in 

 the adult O. rosula, but as a general rule they are rather longer 

 in the stalk. 



If the animal be turned on its back, and examined with a 

 power of 100 diameters by transmitted light, the outline of the 

 stomach is seen to be of a pentagonal form, and has five lateral 

 attachments to the inner surface of the body, which are situate 

 between the rays. The outline of the stomach is dark and well 

 defined, and appears like lines passing from one point of attach- 

 ment to the other; it might be taken at first sight for the 

 nervous system, were it not for the fact, that the meeting of the 

 lines where the nervous threads to the rays would be given off", 

 takes place between the rays, and not at their base, as would be 

 the case if it were the nervous system. 



The contractions of the stomach were very evident ; sometimes 

 the orifice was completely closed, and was then central, and the 

 radiating muscular fibres could be detected. At other times it 

 was dilated quite to the lines indicating the outline of the stomach 

 before mentioned, and at another time much to one side. 



The dilating muscle possesses a great deal more power than 

 the contracting one, as the motion of the former was considerably 

 quicker eff'ected. 



