EMBRYONIC DETERMINATION IN THE ANNELID, SABELLARIA VULGARIS II. TRANSPLANTATION OF POLAR LOBES AND BI.ASK >MKKES AS A TEST OF THEIR INDUCING CAPACITIES ALEX B. NOVIKOFF (From the Department of Zoology, Columbia University and the Marine Biological Laboratory, Woods Hole, Massachusetts] INTRODUCTION E. B. Wilson (1904a) demonstrated that the egg of the annelid, Lanice, belonged to the group of so-called mosaic eggs, since isolated halves of the two-cell stage developed into partial embryos. The anterior cell produced an embryo which lacked the post-trochal region; in the embryo formed from the posterior cell there was present a nearly typical post-trochal region. Delage (1899) had previously described a dwarf embryo from an egg-fragment of the same species. That annelid eggs, generally, are of the mosaic type is shown by the experiments of Penners (1924, 1926) with Tubifex, of Tyler (1930) with Chxtopterus, and of Hatt (1932) with Sabellaria. Wilson (1929) summarizes the evidence which indicates that there is no fundamental distinction between the mosaic and regulative types of ova. Among regulative eggs, where correlative differentiation, or embryonic induction, is most prominent, mosaic features can be found, and in mosaic eggs, there are suggestions that embryonic induction may play a part in early development. Wilson suggests that the polar lobe of such eggs as Dentalium may function as an organizing region similar to the dorsal blastoporal lip of amphibia, since only when the lobe is present does the larva develop the apical tuft and the post-trochal region. However, in the absence of transplantation experi-ments, no final conclusions could be reached. Schleip (1929) describes a "natural experiment" in which a second polar lobe is added to the egg of Dentalium. Among giant eggs, some are found which appear to be fusions of two ova at their vegetal hemispheres. In these eggs, a single large polar lobe may be formed, which goes in its entirety into one of the cells. This leaves one c-u with no lobe, and the other with two. However, such eggs do not develop. Schleip then tried to transplant isolated polar lobes to blastomeres, but all attempts were unsuccessful. 211
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