300 DR. A. MILNES MARSHALL. 



The Morphology of the Vertebrate Olb^actory Organ. 

 By A. MiLNES Marshall, M.A., D.Sc, Fellow of St. 

 John's College, Cambridge. OVith Plates XIII and XIV.) i 



Of the two parts into which the present paper is divided, 

 the first deals with the development of the olfactory nerve in 

 certain selected types of vertebrates ; the second with the 

 development of the olfactory organ in the same types. 



Since the value and interest of anatomical and embryo- 

 logical facts consist largely in their application to the solution 

 of morphological problems, I have not hesitated to draw 

 inferences freely from such facts as I have been able to bring 

 to light, or to point out the conclusions to which these facts 

 seem to me to lead. However, in order to separate facts 

 from theories as sharply as possible, each part of the paper 

 has been farther subdivided, those portions which are con- 

 cerned with matters of direct observation being considered 

 before those which are of a more theoretical or speculative 

 nature. 



I. The Development of the Olfactory Nerve. 



a. In the dogfish. — For the opportunity of investigating 

 the development of Elasmobranchs I am indebted to Mr. 

 Balfour, who, on the completion of his monograph on 

 Elasmobranch fishes, very kindly placed at my disposal the 

 whole of his stock of uncut embryos. In addition to this 

 I have had the great advantage of free access to the very 

 complete series of preparations made by J\Ir. Balfour in the 

 course of his investigations, and have availed myself of his 

 permission to figure four specimens_, illustrating stages of 

 which I had not prepared satisfactory sections myself. 



The greater number of the embryos thus placed in my 

 hands were those of the Scyllmm canicula, some few of 

 Prhtiurus ; but inasmuch as the two genera have yielded 

 identical results so far as the subject in hand is concerned, 

 I have made no attempt to distinguish between them either 

 in my descriptions or figures. Some few of the specimens 

 were hardened in picric acid, and afterwards stained with 

 hsematoxyliu ; but all my best sections were from embryos 

 hardened and stained in a \ per cent, solution of chromic 

 acid, to which a few drops of a weak solution of osmic acid 

 had been added. 



' An abstract of tiiis paper was read before the Royal Society ou Feb- 

 ruary 13tli, 'Proc. Roy. Soc.,' No. 193, 18?9. 



