title: The development of egg-fragments in annelids.
abstract: 1. The unfertilized eggs ofChatopterus, taken near the beginning of the maturation-period, may readily, by strong centrifuging, be broken into fragments of varying size and contents. Both nucleated and non-nucleated fragments of various sizes may be fertilized, and may develop into actively swimming dwarf larvae, some of which approach the normal whole larvae in form, structure and movements. 2. The fragments may contain varying combinations of the three main zones produced by centrifuging, including those derived from the hyaline mid dle zone whicharealmost entirely composed of hyaloplasm. Any of the fragments irrespective of their contents may develop if of sufficient size. 3. The cleavage-pattern of the fragments, irrespective of their contents, closely follows that of the whole eggs, including the size-relations, the alternation of spiral cleavages and the arrangement of the blastomeres. The first cleavage may or may not be accompanied by the formation of a polar lobe, the fragments being probably derived in the first case from the lower hemisphere, in the second from the upper one. In both cases the cleavage is unequal in the normal proportions, and there seems to be only one type of regular cleavage. 4. Since hyaline fragments may segment normally and may produce actively swimming dwarf larvae of nearly normal appearance, it seems probable that the basis of localization, cleavage-patterns, and differentiation must be sought in some kind of internalstructure in the apparently structureless hyoplasm or ground-substance. 5. Some review and discussion is offered of the evidence that the oöplasmic structure is progressively developed and transformed before, during and after cleavage. 6. The relation between mosaic development and embryonic induction or organizing activities is discussed, including some consideration of the question of organizing centers in the "mosaic" types of cleavage.
authors.affiliation: Columbia University, New York.
authors.forename: Edmund B
authors.initials: EB
authors.lastname: Wilson