306 Mr. A. Agassiz on the Young Stages 



surface, so that frequently the examination of a few rods will 

 give us at once what otherwise we should find only after a pro- 

 tracted search. 



' Violent storms, which throw upon the beaches masses of sea- 

 weed, furnish a rich harvest of small animals, attached to the 

 fronds, or concealed between the roots, only to be found in 

 at other times inaccessible hiding-places. The roots of Lami- 

 naria are the resort of thousands of young Echinoderms, Anne- 

 lids, Crustacea, and Mollusks after they have ceased to swarm 

 near the surface of the water, and have assumed somewhat the 

 habits of the adult. Not even the dredge will root these up, 

 and we must snatch at the favourable chances an opportune 

 storm throws in our way. 



I have already shown, in my different papers on the Embryo- 

 logy of Echinoderms* and Acalephsf, how useful knowledge 

 of this kind proved in order to complete missing links in the 

 history of their development. In the following pages will be 

 given some of the results obtained for a few Annelids by a 

 similar mode of procedure. 



Planaria, 



Before the observations of Miiller J on the development of 

 Planarians, the embryos had not been found to differ materially 

 from the adult; according to Siebold§, Schmidt||, and Quatre- 

 fages Tf, they differed principally in size, and no trace of meta- 

 morphosis could be seen ; similar results have been obtained 

 by Van Beneden^*, Keferstein and Ehlersft; and Claparede Jf. 



* " On the Embryology of Astracanthion herylinus, Ag./' in Proc. Am. 

 Acad., April 14, 1863. " On the Embryology of Echinoderms," in Mem. 

 Am. Acad. ix. 1864. " Embryology of the Starfish," in vol. v. of Agassiz's 

 Cont. Nat. Hist, of U. S., 1865. 



t North American Acalephae : No. 2 of Illustrated Catalogue of Mu- 

 seum of Comparative Zoology : 1865. 



X " Ueber eine eigenthiimliche Wurmlarve aus der Classe der Turbella- 

 rien u. aus der Familie der Planarien," in Archiv f. Anat. u. Phys. 1850, 

 p. 485, pi. xii., xiii. 



§ Wirbellose Thiere, in Siebold u. Stannius Vergleichende Anatomic, 

 p. 171. 



II Die Rhabdoccelen Strudelwiirmer des siissen Wassers, beschrieben u. 

 abgebildet: 1848. 



if " Memoire sur quelques Planaires marines," in Ann. Scien. Nat. ser 3, 

 1845, iv. 



** Recherches sur la Faune littorale de la Belgique. Turbellari^s de la 

 cote d'Ostende : I860. 



tt Zoologische Beitriige gesammelt im Winter 1859-60, in Neapel u. 

 Messina: 1861. 



tt Beobachtungen iiber Anatomic u. Entwickelungsgeschichte wirbel- 

 loser Thiere, an der KUste von Norraandie angestellt. Leipzig, 1$63. 



