STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 739 



THE ALIMENTARY CANAL AND ITS APPENDAGES PAGE 



Topographical anatomy of the alimentary canal 828 



Development of the alimentary canal and its appendages . . . 831 



THE GILL ON THE HYOID ARCH 835 



THE SYSTEMATIC POSITION OF LEPIDOSTEUS . . . . . . 836 



LIST OF MEMOIRS ON THE ANATOMY AND DEVELOPMENT OF LEPIDOSTEUS 840 



LIST OF REFERENCE LETTERS . . . . 841 



EXPLANATION OF PLATES 842 



INTRODUCTION. 



THE following paper is the outcome of the very valuable gift 

 of a series of embryos and larvae of Lepidostens by Professor Alex. 

 Agassiz, to whom we take this opportunity of expressing our 

 most sincere thanks. The skull of these embryos and larvae has 

 been studied by Professor Parker, and forms the subject of a 

 memoir already presented to the Royal Society. 



Considering that Lepidosteus is one of the most interesting of 

 existing Ganoids, and that it is very closely related to species of 

 Ganoids which flourished during the Triassic period, we naturally 

 felt keenly anxious to make the most of the opportunity of 

 working at its development offered to us by Professor Agassiz' 

 gift. Professor Agassiz, moreover, most kindly furnished us with 

 four examples of the adult Fish, which have enabled us to make 

 this paper a study of the adult anatomy as well as of the develop- 

 ment. 



The first part of our paper is devoted to the segmentation, 

 formation of the germinal layers, and general development of the 

 embryo and larva. The next part consists of a series of sections 

 on the organs, in which both their structure in the adult and 

 their development are dealt with. This part is not, however, in 

 any sense a monograph, and where already known, the anatomy 

 is described with the greatest possible brevity. In this part of 

 the paper considerable space is devoted to a comparison of the 

 organs of Lepidosteus with those of other Fishes, and to a state- 

 ment of the conclusions which follow from such comparison. 



The last part of the paper deals with the systematic position 

 of Lepidosteus and of the Ganoids generally. 



