Biology of Bryozoans by Robert M. Woollacott

By Robert M. Woollacott

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27e-g). Silén called this an ectooecium. The inner prominence forms a sac which partly fills up the space in the hood; this Silén calls an endooecium (Fig. 2Ί\ϊφ2)- Some authors interpret the endooecium as being the inner wall of the ectooecium and they simply call the inner protuberance the inner vesicle. Here I have used Silén's interpretation. Fig. 25. Hypothetical diagram of the relationship between an outer embryo sac and the ovicell. Redrawn from Silén (1944). (a) Labiostomella gisleni, outer embryo sac; (b) hypothetical intermediate form; (c) ovicell at the distal part of the zooid; (d) the hyperstomial ovicell; (e) the endozooidal ovicell.

At this stage the larva leaves the embryo sac through an opening which is formed in the outer part of the sac's epithelium. The larva is lecithotrophic and largely modified compared with a planktotrophic larva. It can be described as a small colony. At emergence the larva first rotates 180° so that it swims out backward. The posterior pole will then lead when swimming. Phylogenetically this reversal probably is of secondary origin (Jägersten, 1972). The folding-up of the mantle over the developing polypide buds of the larva is suggestive of the cyclostome larva.

25. Hypothetical diagram of the relationship between an outer embryo sac and the ovicell. Redrawn from Silén (1944). (a) Labiostomella gisleni, outer embryo sac; (b) hypothetical intermediate form; (c) ovicell at the distal part of the zooid; (d) the hyperstomial ovicell; (e) the endozooidal ovicell. 40 Rolf Ström Fig. 26. The transfer of the ovum to the ovicell in Callopora dumerilii. Redrawn from Silén (1945). (a) The ovum at the distal end of the zooid; (b) the polypide in extended position; (c) the ovum lies near the supraneural pore; (d) the ovum flows into the ovicell; (e) the ovum or zygote lies in the embryo chamber.

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