he Ecliiiioid, siicli as it is when it lias just ended its larval 

 period and assiimed tlie outward form of tlie adult, has been 

 described from time to time, tlie Arbacia fequituberculata Bi,v. 

 and the A. punetulata Lamck by Johannes Muller \ Alex- 

 ander Agassiz^ and GtARMAN and Colton^; the Strongylocentrus 

 dröbakensis O, F. M. by Al. Agassiz*; the Strongylocentrus 

 lividus Lamck by Krohn-^; the Echinus parvitnbercnlatns Blv. 

 by BuRY^; the Echinarachnius Parma Lamck by Fewkes^ 

 and besides these other' doubtful or unknown species^. I for- 

 meri}' observed a young specimen of some northern forra^. 

 and had the drawings made wliich are repeated here p. 11. 



In these several instances the hnal form takes its existenee 

 not from an egg but from the interiör of a larva, the pln- 

 teus, Avhieh is itself the direct issne of an egg and after 

 a short free-swimming life has its frame consumed in ori- 

 ginating the imago. From tliis general process of indireet 

 development two exceptions are known in whieh the free- 

 swimming stage is left ont, be it that surrounding agencies 

 in some manner have rendered the metamorphosis snperfluous, 

 perhaps dangerous, or that they represent an order of things 

 else antiquated, or a new era of simplified development. They 

 are: a Spatangid, Abatns cavernosus Phil. ^", and a Cidarid, 



' Metamorpliose d. Echinodcrmen, YII, 1855, p. 22, Pl. IV, fig. 3. 4. 



2 Revision. 1.S74, p. 734, fig. G8. »59. 



' Brooks, Handbook of Invertebrate Zoology, 18<S2, p. 130. fig. 76, 77. 



* Embrvologv of Echinoderms. Mem. Amer. Acad., IX. 1861, pl. 1; Revi- 

 sion, p. 709, 'PL IX, fig. 1; Pl. X, fig. 1-4. 



* Mullers Archiv, 1851, p. 351. 



« Quart. Journ. Microsc. Science, N. S., XXIX, p. 439, Pl. XXXVIII, fig. 11. 

 ' BulL Mus. Comp. Zool., XII. p. 120. Pl. II— VIII, 1886. 



* Johannes Muller. Jletamorphose, I, 1848. p. 23, Pl. VII, fig. 1 — 11. 

 Ib., VII, 1855. p. 2S. Pl. VIII, fig. 8—10. 



9 Etudes s. 1. Echinoidées, 1874, p. 27, Pl. XVII. fig. 149 152. - Pour- 

 talesia, p. 25, Pl. XIX, fig. 232, 233. 



'" Philippl Wgm.. Arch.. XI. 1845. p. 346. — Al. Agassiz, Proc. Amer. 

 Acad., XI, 1876, p. 231; Challenger Ech;, 1881, p. 179, Pl. XX% fig. 1, 2. 7— 

 10. — Wyv. Thomson, Vov. Cliall.. II. 1877, p. 229, woodcut p. 233. Stu- 

 DER. Berlin. Mon. Ber., Juli 1876, p. 457; ib.. Ootober 1880, p. 881; Zool. An- 

 zeiger. 1880, p. 67, 68. 



