CURIOSITIES OF STAR-FISH LIFE. 



361 



and sea-urchins, or more particularly to the nervous systems, and the 

 movements controlled by them, in these creatures. 



A star-fish, as we all know, consists of a central disk and five radi- 

 ating arms (Fig. 1). Upon the whole of the upper surface occur 

 numerous calcareous nodules imbedded in the soft flesh, and support- 

 ing short spines. One of these nodules, much larger than the others, 

 is always found a little to one side of the center, and is called the 

 madreporic tubercle (Fig. 1, m). With the aid of a lens we may see 

 also on the upper surface a number of small organs, each consist- 

 ing of a pair of pincers supported on a flexible stalk, scattered about 

 among the calcareous nodules, or attached to the spines ; these are 

 known as pedicellariae (Fig. 2). These organs are provided with mus- 

 cles' by which the stalk is swayed about, and the pincers are opened 

 and shut. What it is that these cm-ious organs are adapted to seize, 

 and therefore of what use they are in the economy of the animal, has 

 long been a puzzle to naturalists, but Dr. Romanes and his associate, 

 Professor Ewart, have succeeded in throwing some light on this point. 

 In some species of star-fish the size of the central disk is increased so 

 as to fill up the spaces between the rays, the form of the animal thus 

 becoming a pentagon. In other species the reverse process has taken 

 place, the rays having become relatively longer, and, being at the same 



Fig. 3. A Brittle-stab. (From Cassell'e " Natural History.") 



time very active, they look like five little snakes joined together by a 

 small circular disk (Fig. 3). Again, in another species the rays branch, 

 these branches again branch, and so on till the animal looks like a mat. 

 Turning now the under surface of our star-fish uppermost, we see that 

 the mouth is in the center of the disk, and that from the mouth radiate 



