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 this 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 complete 

 thin envelope around it. In many ova, e. g. those of many 

 species of the Gradidae and Pleuronectidge, 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 (Trigla) and mackerel {Scomber scomber) , 

 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), 



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