FORCIPULATA 473 



As mentioned above, Ludwig has proved that the paxillae 

 develop in the life-liistory of the individual out of ordinary 

 plates, the axis of the paxilla reja-esenting the plate. 



Order V. Forcipulata. 



This order, which includes the most highly developed mem- 

 bers of the class Asteroidea, is at once distinguished by the 

 possession of forcipulate pedicellariae which, as we have seen, 

 possess a well-marked basal piece with which the two plates 

 articulate. The pedicellariae are consequently sharply marked 

 off from the spinelets, and no intermediate forms occur. The 

 first conjoined adambulacrals, which in other orders form the 

 " teeth " or mouth-angles, do nut here project beyond the first 

 pairs of ambulacral plates. 



Fam. 1. Asteriidae. — Forcipulata in which the tube-feet are 

 apparently arranged in four rows. Aljoral skeleton a loose 

 reticulum. 



The general features of the family Asteriidae ha^'e been ex- 

 plained in the description of Asterias ruhens (p. 432). There are 

 five well-marked species of the genus found on the British coasts. 

 Of these A. glacialis is found chiefly in the south-western parts of 

 the English Channel. It is a large Starfish of a purplish-grey 

 colour, with large spines surrounded by cushions of pedicellariae 

 arranged in one or two rows down each arm. A. mueUeri 

 resembles the foregoing species, but is of much smaller size, and 

 is further distinguished by having straight pedicellariae in the 

 neighbourhood of the ambulacral groove only. It is found on the 

 east coast of Scotland, and carries its comparatively large eggs 

 about with it until development is completed. A. ruhens is the 

 commonest species, and is found on both east anil west 

 coasts. Its colour is a l)right orange, but varies to almost a 

 straw colour. It is at once distinguished from the foregoing 

 species by the spines of the dorsal surface, which are small and 

 numerous, an irregular line of somewhat larger ones being some- 

 times seen down the centre of each arm. A. murrayi is a 

 peculiar species restricted to the west coast of Scotland and 

 Ireland. It has flattened arms, with vertical sides, and only 

 three rows of small spines on the dorsal surface. It is of a 

 violet colour. A. Iiisjnda is also a western species. It is a 



