NOTES ON L.M.B.C. ASTEROIDEA. 141 



ossicles each one gives off on either side a great number 

 of lateral branches which open into the cavities of the 

 tube-feet. The fluid which occurs in these vessels contains 

 ajnoeboid corpuscles. Of the tube-feet there are two 

 usually straight, but in Aster las sharply zig-zaged rows, 

 lodged in the ambulacral grooves. Each tube-foot is 

 provided with a vesicular ampulla lodged within the cavity 

 of the ray. Communication between the two is established 

 by a canal w^iich passes upwards from the base of the 

 foot through a corresponding pore formed by grooves in 

 the two adjacent ambulacral ossicles. In many genera the 

 tube-feet terminate in sucker-discs, but those oi Astropecten 

 and Luidia are conical at their free ends. 



The nervous system consists of a plexus of nerve fibrils 

 and ganglion cells which underlies the ectoderm. At the 

 bottom of the ambulacral grooves the fibres are much 

 more numerous, and run parallel w^th the axis of the ray. 

 In transverse sections they appear as minute dots between 

 the filiform inner ends of the ectoderm cells, which are 

 here enormously elongated, and form a ridge-like thicken- 

 ing, the ambulacral nerve. Each radial nerve joins its 

 fellows on either side to form the cn'cum-oral nerve-ring 

 (PL XXXYIII, figs. 1 and 3, nr). The generative organs 

 consist of sacculated glands, of which there is a pair in 

 each ray. Each gland is attached to the lateral wall of 

 the ray, near its base, and opens by a single pore, or 

 rarely by a number of pores. In the genus B rising a each 

 ray contains a number of distinct glands, arranged serially 

 along each side of the ray, and opening by separate pores. 



Having thus briefly surveyed the general organisation 

 of starfishes, I now proceed to a discussion of the minute 

 anatomy of the two systems mentioned at the outset. 

 Careful examination of a large number of sections of the 

 madreporite of Asterias, Crihrella, Astropecten and Aste- 



