CONSIDERATIONS ON CELL‐LINEAGE AND ANCESTRAL REMINISCENCE: BASED ON: A R e ‐E xamination of S ome P oints in the E arly D evelopment of A nnelids and P olyclades .

1 Von Wishghawn ( 1@1 1 Iud previously observed in Nreir Bwiurihi, n p u p of small cells derived from the "second somatoblast," which probably correspond with thoOK I hnve described in N. /inibnlo and N. nieguhpr, though their exact mipin w u not followed.Wirtinghnusen believed that they gave rise to n part of the ectoblut--1 result wholly ditTerent from Loth my enrlier.nccountand the present one.*Minute cells exactly corresponding in origin and number to those of Aricia have k e n found by Mead in Aviphifrite (I&, p. 467 ; 1897, p. 247) and by Holmes ip P/flirorlir (1897, p. 101).Iillir hns found n pnir of corresponding but slightly IarKer cells in Urio (1895, p. 1 7 ) , while in Cly,netit//n they arc DS large as the primary mesoblmts (Mead, 1897, p: '264).The corresponding cclls in Uitbrt//,a (Heymons), Crepidtda (Conklin), and Phym (Wienejski) will he referred to beyoud (see pp. 6, 11-12). 1 Ntrtis, p. 413. 61897, p. 101.'18g5, p. 28.