D. C. McIntosh 



473 



ru^s, ;ui(l tlicrc was also a single spepinieii witli lour rays (scc Fig. S), pcrfoct 

 in every way. lu tho third thoiisaiHl tlicio wure three .speciineiis with six rays — 

 all of which were, howevcr, unt'oi tuiialcly coiisiderably (laniapcd. Theii! is thus 

 Iht'U k'ss thau oiic-half per ceiit. of duviation f'roin the iKirinal five rays. Are 

 those deviatidiis nientidiied Id l)i' lookcd upou as* " abimiiiial variations," or 

 nierely as " very iiitVequent iKjrnial variations"? 



5. As to the nuiiiher of inadreporic jüates. 



The ma(h'eporitc, even in ophiuroids fresh froni water or f'roni alcolioi, bat 

 especially in dvy speciniens, is very easily seen. Its position, shape, size, and 

 colour readily assist one in findiug it. Caref'ul Observation, even without a 

 niicroscope, shows that it is perforatcd, but I do not think the perforations are 

 nearly so nnnierous as seems to be generally supposed. Its colour, a delicate 

 yellow, is distinctly lighter than that of the othcr plates in the angle between the 

 rays. It is also larger and its heart-shape is characteristic. In my observations 

 I found in all thirty-nine speciniens which had two or niore of the plates so 

 like the madreporite that one conld not teil the real niadrcporic plate. This 

 peculiarity, I find, has been noted by Jeffrey Bell, who says that "in ophiuroids 

 the stone-canal ends on one or several of the inoutli shields." While it is true that 

 there is nornially but one madreporic plate, and it niay be presumed there can be 

 only one stone-canal, yet to all appearance niore than one niouth-sliield niay 

 be capable of performing the function of a inadreporic plate. Table V. gives 

 not only the nuniber of speciniens in the three thousand with more than one 

 madreporic plate, but shows how the plates were situated in relation to each other. 

 The relative percentages in the first, second, and third thousands are worthy of 

 notice, there being on the average 013 speciniens abnormal. 



TABLE V. 



SliiDi'iiiff the Xuinher und Relative Positiun of Madreporites. 



The Granimar <if Science, p. 390. 



