XXII. On the Structure and Development of Lepidosteus[498].
By F. M. Balfour and W. N. Parker.
(With Plates 34-42.)
[498] From the Philosophical Transactions of the Royal Society, 1882.
| TABLE OF CONTENTS. | |
|---|---|
| PAGE | |
| Introduction | [739] |
| General Development | [740] |
| Brain— | |
| Adult brain | [759] |
| Development of the brain | [764] |
| Comparison of the larval and adult brain ofLepidosteus, together with some observations on the systematic valueof the characters of the Ganoid brain | [767] |
| Sense Organs— | |
| Olfactory organ | [771] |
| Anatomy of the eye | [ib.] |
| Development of the eye | [772] |
| Suctorial Disc | [774] |
| Muscular System | [775] |
| Skeleton— | |
| Vertebral column and ribs of the adult | [776] |
| Development of the vertebral column andribs. | [778] |
| Comparison of the vertebral column ofLepidosteus with that of other forms | [792] |
| The ribs of Fishes | [793] |
| The skeleton of the ventral lobe of the tailfin, and its bearing on the nature of the tail fin of the various types ofPisces | [801] |
| Excretory and GenerativeOrgans— | |
| Anatomy of the excretory and generative organsof the female | [810] |
| Anatomy of the excretory and generative organsof the male | [813] |
| Development of the excretory and generativeorgans | [815] |
| Theoretical considerations | [822] |
| The Alimentary Canal and itsAppendages— | |
| Topographical anatomy of the alimentarycanal | [828] |
| Development of the alimentary canal and itsappendages | [831] |
| The Gill on the HyoidArch | [835] |
| The systematic position ofLepidosteus | [836] |
| List of memoirs on the Anatomy andDevelopment 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 larvæ of Lepidosteus by Professor Alex. Agassiz, to whom we take this opportunity of expressing our most sincere thanks. The skull of these embryos and larvæ 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 development.
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 statement 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.