Parts of the Lantern of Aristotle in Echinus miliaris. 483 



of his observations. He boiled the root-end with caustic-potash, a treatment 

 which undoubtedly would have interfered with the structure of such delicate 

 things as the lamella;. The wonder is that Giesbrecht accomplished so much 

 with the methods at his disposal in those days. 



10. Summary. 



(1) All the calcareous elements of the lantern of Aristotle, with the 

 exception of the teeth, are deposited as tri-radiate spicules ; in this, as well as 

 in their further growth, they resemble the ossicles of echinoderms in general. 

 • (2) The two " epiphyses," one on each side of and below a rotula, are to be 

 regarded as constituting a pair. 



(3) A " compass " arises from two rudimentary spicules. It is the only 

 element of the lantern absent in the " echinus-rudiment." 



(4) A tooth is a paired structure in consequence of its composition of a 

 double row of lamella?. A pair of lamella? is its ultimate unit, although it is 

 not inconceivable that originally a pair of lamella? itself, after assuming a 

 cone-shape, could have functioned as an integral structure, a primitive kind of 

 tooth, in the ancestral urchin. There is a remarkable stage in the consolida- 

 tion of these lamella', viz., the cone-in-cone arrangement. The carina is 

 formed by the beaks of the serially-fitting cones. 



(5) Without committing one's self to the view of a direct descent of the 

 sea-urchins from the star-fishes, one may institute a brief comparison between 

 the ossicles of the lantern and those of the mouth-frame of a star-fish : a pair 

 of " alveoli " corresponds to a pair of mouth-angle plates ; a pair of 

 " epiphyses," as understood in this paper, to the first pair of ambulacrals ; 

 a pair of compasses to the second pair of ambulacrals ; the rotula may, 

 tentatively, be regarded as. a displaced odontophor; the pair of primordial 

 lamella?, the forerunner of the urchin-tooth, may be compared to a pair of 

 bristles attached to a pair of mouth-angle plates. 



11. REFERENCES. 



(1) Giesbrecht, W. (1880). " Der feinere Ban tier Seeigelziihne," ' Morph. .Tahrlmch,' 



vol. 6. 



(2) Jackson, R. T. (1912). "Phylogeny of the Echini/' 'Mem. Bos. Soc. Nat, Hist.,' 



vol. 7. 



(3) Loven, S. (1892). " Echinologica," ' Bihang Kongl. Sven. Veten. Akad. Handl.,' 



vol. 18. 



(4) MacBride, E. W. (1903). " The Development of Echinus esculentus, together with 



some points on the development of E. miliaris and E. acutus" ' Phil. Trans. Roy. 

 Soc.,' B, vol. 1 95. 



