. The Biological bulletin. Biology; Zoology; Marine biology. 68 EDWARD L. (Figs. 4, C'; 4, i7), and may be followed readily into the charac- teristic filaments of their respective gills (Figs. 2 and 3). In this connection it should be strongly emphasized that the filament anlagen here described are by no means the equivalent of the papillae described by Lacaze- Duthiers, although their appear- ance in such a stage as that figured in Fig. 4, D, is strikingly similar. The undivided transverse fold (Fig. 4, A) contains potentially an entire filament of each gill; and each of its subdivisio
. The Biological bulletin. Biology; Zoology; Marine biology. 68 EDWARD L. (Figs. 4, C'; 4, i7), and may be followed readily into the charac- teristic filaments of their respective gills (Figs. 2 and 3). In this connection it should be strongly emphasized that the filament anlagen here described are by no means the equivalent of the papillae described by Lacaze- Duthiers, although their appear- ance in such a stage as that figured in Fig. 4, D, is strikingly similar. The undivided transverse fold (Fig. 4, A) contains potentially an entire filament of each gill; and each of its subdivisions (Fig. 4, D) is the equivalent of the two limbs of a filament placed side by side. On the other hand, the earlier type of anlage must be considered as the equivalent of only one limb of the definitive filament, or perhaps better, of the two placed end to end. In the earlier type the reflexed limb of the filament originates through a bending of the anlage; in the later type there is no bending, but rather a longitudinal splitting. The exact details of this splitting and the formation of the cavity within the gill, shown in Fig. 4, E, have not been worked out; but a study of a series of specimens such as those represented in Fig. 4 makes it clear that the process consists essentially in a thinning and ultimate perforation of the plate-like anlage of Fig. 4, D. Corroborative evidence as to the nature of these later filament anlagen and their distinction from the earlier and more anterior ones is found in the character of the ciliation. A comparison of Figs. 4 and 5 is instructive in this connection. Fig. 5 is drawn from a section; but the filaments of the gills have been slightly reconstructed from neighboring sections, so that they are repre- sented in their entirety. This represents an earlier filament of the outer gill (Fig. 5, b), with its characteristic rod-like form. Details of the ciliation have been omitted except for the some- Fig. 3. Posterior tip of ctenid- ium of Myt
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectb, booksubjectzoology
