MADREPORIFORM BODY. 17 



In all the EcH(NiD.E the inadrcporiform body is single, and rests on the upper surface 

 of the right antero-lateral ovarial plate ; sometimes, however, it extends over the other 

 elements of the apical disc, and surrounds them with its spongy structure. In the 

 AsTERiAD^ the madreporiforni plate is likewise for the most part single, but there are 

 many species in which two, three, or more plates are found. It has been assumed that an 

 increase in the number of the plates bears a certain relation to the number of the arms ; 

 observation, however, has proved that this is not the rule in all the many-rayed forms. 

 Solaster and Luidia, for example, which possess numerous rays, have the madreporiforni plate 

 single, whilst in some five-rayed Ophidiasters the plate is double. With an increased number 

 of arms there is, in some genera, a corresponding increase in the number of the madrepori- 

 form plates. Thus, in Asterias Helianthus, Lamk., which has from thirty to thirty-six rays, 

 the madreporiform plate consists of many pieces; and Uraster tenuispina, Lamk., which 

 has from six to eight rays, possesses two or three plates. The genera Ophidiaster and 

 Echinaster, in general, have more than one plate. In OpJiidiaster multiforis, Lamk., 

 the individuals with five rays have two plates, whilst those with six rays have three ; 

 and in 0. diplax, 0. ornithopus, 0. Ehrenbergii, all five-rayed species, there are two plates 

 in each. The remarkable Echinaster Solaris, so beautifully figured by Ellis,^ has twenty 

 short rays armed with very long spines, and around the circumference of the anal area 

 sixteen hemisphei'ical, madreporiform plates are figured ; in other individuals of the 

 same species, examined by Miiller and Troschel,^ the number of plates was not so great ; 

 one specimen with fourteen rays had five, and another with sixteen rays had six plates ; 

 and Echinaster Eridanella, Valenc, with six rays, has two madreporiform plates. In 

 those genera, therefore, the number of the plates appears to augment with the number of 

 the rays. 



The Tegumeniary Appendages. 



The tegumentary membrane in the Asteriad^ is provided with difi'erent kinds of 

 appendages, as spines, granules, paxillce, and Pedicellaria, each of which requires a sepa- 

 rate notice. 



The spines are calcareous pieces of various forms and sizes ; they are in general 

 attached by their base, and often destitute of the kind of articulation seen in the 

 spines of Echinid^. In Uraster, PI. I, fig. 2, they are sharp, prickly processes arranged 

 in rows, with more or less regularity, along the upper surface, sides, and base of the rays. 

 In Astropecten (fig. 3) and Luidia (fig. 6), they are in the form of long, tooth-like spines 

 which project from the sides of the marginal plates. In Pteraster (fig. 5) they fringe the 

 borders of the rays, form fan-like semicircles near the ambulacra, and arm the upper 



1 'Natural History of Zoophytes,' p. 206, PI. 60, 61, 62. 



2 ' System der Asteriden,' p. 25. 



