Embryology of certain of the Lower Fishes. 191 



XV. The Embryology of certain of the Lovjer Fishes, and its 

 Bearing upon Vertebrate Morphology. By J. GRAHAM 

 Kerr. 



(Read 27th February 1905.) 



Introduction. 



The worker who takes up seriously the study of Vertebrate 

 Morphology cannot, as it seems to me, avoid being much 

 impressed by certain limitations to which one important 

 side of his subject — the embryological side — is subjected. 

 These limitations are due to the fact that the foundations 

 of the science of embryology have been laid, not on the 

 comparison with one another of the developmental pheno- 

 mena shown by the more lowly organised vertebrates, but 

 on the features of development as they occur in a few easily 

 accessible and easily investigated forms — the chick, the 

 rabbit, the selachian, and, to a much less extent, the 

 frog. The first three of these — and they have played by 

 far the greater part in building up the science of embryology 

 — are all of them forms in which there is present, or appears 

 to have been present in the ancestral forms, an enormous 

 mass of food-yolk, which cannot have been without a 

 marked distorting influence on the course of development. 



Considerations of this kind led the author some years 

 ago to devote himself to a study of the development of 

 certain of the lower forms of vertebrates ; and, in the present 

 communication, it is proposed to draw the attention of the 

 Society to some of the embryological features of these forms, 

 which may be regarded as having a bearing upon the general 

 morphology of the Vertebrata. 



The work has been carried out upon the Dipnoans, Lepido- 

 siren and Protopterus, with Ceratoclus and various Urodeles 

 for comparison, and more recently on the Crossopterygian 

 ganoid Folypterns} 



•^ Owing to the lamented death of my friend Budgett. A detailed account 

 of the development of Polyjpterus will be found in the forthcoming Budgett 

 Memorial Volume. 



VOL. XVI. S 



