Fig. 4 in Reproductive biology, embryonic development and matrotrophy in the phylactolaemate bryozoan Plumatella casmiana

Fig. 4 Gonads and early embyo sac of Plumatella casmiana (semithin sections a, c, d), and whole-mount of Plumatella sp. (b). a Ovary with several oocytes. b Testes at the funiculus. Spermatids contain mostly the nucleus (insert). c Early cleavage stage with an embryo consisting of several blastomeres located at the free end of the embryo sac. The maternal ectodermal lining of the embryo covers the entire embryo (dashed line). d Oblique section of a blastula stage with commencing mesoderm formation (arrowheads indicate first mesodermal cells delaminating from the ectoderm). The maternal ectodermal lining persists (dashed line). Abbreviations: bwm body wall musculature, e embryo, ebs embryo sac, ed epidermis (ectodermal origin), ese embryo sac ectoderm, esm embryo sac mesoderm, fu funiculus; mec maternal ectoderm cells, nu nucleus, nuc nucleolus, ooc oocytes, ov ovary, ovc follicle cell, p peritoneum (mesodermal origin), sp sperm, yd yolk droplets