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Show 1^86.] ON SQUALORAJA POLYSPONDYLA. 527 body (Plate LII. fig. 1) in a later stage. Lettering as in last plate. Fig. 7, 8. Transverse sections through a portion of outer surface of multicellular body in a later stage, a, degenerating nuclei; other lettering as before. 9. Multicellular body from ovum of Protopterus, differing from that illustrated in fig. 1 mainly by the absence of follicular layer. Lettering as before. 10. Portion of secondary follicular layer at point marked with an arrow in preceding figure ; more highly magnified. 11. Central mass of a body belonging to same stage as that figured in fig. 9, to show the mass (p) formed by the breaking down of the central cells (c), the nuclei of which (n) are here and there imbedded in it. 12. One of central cells (Plate LII. fig. l,c) with a large number of nuclei. 13. Three central cells from Stage I. (fig. 1, b), to show difference in nuclei. 14-20. Central cells very much enlarged from Plate LII. fig. 1, to show tbe different stages in degeneration of nuclei. 21. Nest of germinal cells in ovary of Ceratodus at a later stage than that in Plate LII. fig. 3. Lettering as in that figure. PLATE LIV. Fig. 22. A portion of body represented in Plate LIII. fig. 21, more highly magnified. Lettering as in fig. 21. 23. Nest of germinal cells in ovary of Ceratodus at a stage near to that represented in figs. 21 and 22. Lettering as in those figures. 24. Portion of multicellular body in ovary of Protopterus, to show masses of yolk (a), apparently corresponding to areas occupied by fused masses of protoplasm in earlier stages (p in figs. 1, 9, and 11). 25. Multicellular body of Ceratodus at a stage corresponding to that of Protopterus, illustrated in fig. 1. a, fibrous tissue of stroma-layer; other lettering as in fig. 1. 26. A portion of central cells of multicellular body of Ceratodus, more highly magnified. Lettering as in fig. 1. 27-31. Central cells of multicellular body of Protopterus at an early sta°-e, to show commencing yolk. 32, 33. Central cells of ditto, to show disintegrating nucleus. 2. On. the Anatomy and Systematic Position of the Liassic Selachian, Squaloraja polyspondyla, Agassiz. By A. S M I T H W O O D W A R D , F.G.S., of the British Museum (Natural History). [Received October 18, 1886.] (Plate LV.) SUMMARY OF PREVIOUS RESEARCHES. The prolific fish-beds of the Liassic formation have yielded so much valuable material during recent years, that it is now possible to considerably supplement the original anatomical memoirs of Agassiz, Egerton, and the other pioneers in early Mesozoic ichthyology. Many specific types that were at first only known from very |
