d6 



LIFE, IN ITS LOWER FORMS. 



But between the Feather-star and the Sea-urchin there 

 is so great a diversity in form and appearance, that our 

 readers may be reluctant to admit them into the same 

 category ; the gulf that separates them seems to be 

 too wide. Let us see however, if we cannot bridge it 

 over. 



If you have ever thrown a dredge overboard in any of 

 our quiet bays a mile or two from shore, and examined 

 the host of curious and strange things which it has brought 

 up from the floor of the sea, you know what a Brittle-star 

 is. But if not, we will try to describe it for you. We 

 select the commonest species, — Ophiocoma rosida, the 

 Rosette. Imagine a central disk about as large as a silver 

 fourpenny-piece, of a form between a circle and a pentagon, 

 composed of five pairs of triangular plates pointing towards 

 the centre, and separated by bands of leathery skin stud- 

 ded with minute spines. In the centre of the under 

 surface of the disk is the mouth, an aperture into which 

 project five complex plates, and from whose margin spring 

 five long slender rays diverging on every side, and looking 

 much like the tails of so many scaly lizards. 



Now these rays are of exquisite workmanship. They 

 appear to be nearly solid columns, with narrow tubular 

 canals running through them ; but they are penetrated 

 by various organs, with muscles for motion, with glands 

 for secretion, with nerves for sensation, and so forth. Ex- 

 ternally they are seen to be built up of plates, which fit 

 and partly overlap one another, so as to allow great free- 

 dom of motion. Those on the upper side are triangular, 

 with blunt points ; those beneath are square, with the 

 corners cut off. These two series are connected by lateral 



