. Biological lectures delivered at the Marine Biological Laboratory of Wood's Holl [sic]. Biology. Fig. 19. — Scolecolepis, 28-ceIl stage, from left side. Shaded like figures of Aviphitrite. regard to the origin of the prototroch, however, it must be admitted that, according to von Wistinghausen's account, this orsan is formed from cells which do not correspond with any of the trochoblasts of other annelids. His account places us in the same predi- cament with regard to the ori- gin of the prototroch as with regard to the origin of the primary mesoblast cell. In respect to both, if the account
. Biological lectures delivered at the Marine Biological Laboratory of Wood's Holl [sic]. Biology. Fig. 19. — Scolecolepis, 28-ceIl stage, from left side. Shaded like figures of Aviphitrite. regard to the origin of the prototroch, however, it must be admitted that, according to von Wistinghausen's account, this orsan is formed from cells which do not correspond with any of the trochoblasts of other annelids. His account places us in the same predi- cament with regard to the ori- gin of the prototroch as with regard to the origin of the primary mesoblast cell. In respect to both, if the account is correct, Nei'eis Diininierillii is unique. In order to bring this annelid into line with the others, most writers on cell- lineage have expressed doubt, and rightly I think, as to the accuracy of the account in the case of the mesoblast. The origin of the mesoblast cell, however, is definitely described by von Wistinghausen, while he did not even pretend to work out the prototroch cell by cell. So we may, perhaps, be permitted at least to sus- pend judgment in regard to the discrepancy in the origin of the prototroch in this species. In those annelids in which the trochophore is still farther suppressed, and which undergo a direct development, , in Rhynchelmis and Clepsiue, the anterior quartette in the 8-cell stage is still farther reduced. Fig. 22 is from an unpublished drawing of Clepsiue, 8-cell stage, given me by Dr. Whitman. We may say in general of all the forms which we have. Fig. 20. — Scolecolepis, 2S-celI stage, from anterior Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Marine Biological Laboratory (Woods Hole, Mass. ). Boston, Ginn & Co
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