On some Disputed Points in Teleostean Embryology. 203 XXIII.^ — On some Disputed Points in Teleostean Embryology. By J. T. Cunningham, M.A., Naturalist to the Marine Biological Association. At the time when Balfour wrote his ' Comparative Embryo-logy ' less was known concerning the development of the Teleostei than concerning that of any other class of the Verte-brata. But since that time explorations in this field have been very numerous, and the results obtained have not only brought our knowledge of Teleostean development up to the level of that of the embryology of Elasmobranchs, but have in many cases given quite a new meaning to processes pre-viously observed in the development of other types. Inter-pretations and conceptions that appeared satisfactory when founded on a comparison of Elasmobranchs, Amphibia, and Sauropsida have been found to be inconsistent with the phenomena presented by Teleostean ova, and have therefore had to be either modified or abandoned. But the absence of anything like sound criticism in biology allows all the nume-rous memoirs and papers that have been published on the subject during recent years to claim equal authority, although there is little agreement or harmony among them. My purpose in tliis paper is to draw attention to the points which have been firmly established by satisfactory evidence and to distinguish the sound from the unsound among recent descrip-tions and arguments. The Structure of the Mature Ovum. The ovum at the moment it leaves the oviduct of the female consists of the ovicell enveloped by a capsule or membrane which is everywhere in contact with it. The ovicell consists of a small quantity of protoplasm and a larger quantity of nutritive material or deutoplasm. In the usual type of pelagic ovum the deutoplasm forms a continuous homogeneous mass which is transparent, and the protoplasm forms a comj)lete thin envelope around it. In many ova, e. g. those of many species of the Gadidaj and Pleuronectidae, there is no other element in the ovicell than the pellucid yolk and the peripheral pellicle of protoplasm ; but in many other pelagic ova, e, g. those of the gurnard [Irigla) and mackerel {Scomber scomber) y there is in addition a somewhat large globule of oil. In some ova there are numerous oil-globules. Professor W. C. M'Intosh, in his review of my ' Treatise on the Sole ' (11), 14*
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