■538 STRUCTUKE OF THE LARVAL POLTPTERUS. 



Whatever be the true interpretation of the genital duets in the Ichthyopsida, the 

 Crossopterygii, Teleostei, and Ganoidei are closely united in this respect, the latter group 

 appearing to stand in closer relationship to the rest of the Gnathostomata than the 

 former groups. 



V. — Conclusion. 

 We have seen, then, that in its development Polypterus shows affinities in various 

 directions. The development of the pectoral fin and of the cranium and visceral arches 

 has some resemblance to that of the Elasmobranchii, while of course the spiral valve, the 

 conus and optic chiasma in the adult are other structures common to the two groups. 

 The development of the vertebral column is not very dissimilar to that of the Teleostei, 

 though in the possession of lateral cartilaginous processes in addition to the neural and 

 ventral processes of the Dipnoi, Ganoi<lei, and Teleostei, Polypterus presents a very 

 generalized condition ; while there can be no doubt that from the standpoint of 

 urinogenital organs both the larval and adult Polypterus are as closely connected with 

 the Teleostei as even Amia itself. It has, however, been admitted by the most 

 competent palteontologists that the structure of the dermal bones of the head and of 

 the shoulder-girdle of Polypterus is so like that of certain Stegocephali, that it must be 

 regarded as more than a mere resemblance, while there are many points in the 

 development of the skeleton that distinctly approach the condition of the Amphibia. 

 The only possible interpretation of these facts appears to me to be that the living 

 Crossopterygians form a central group among recent forms having some characters in 

 common with most of the great groups. Seeing that it is thus a generalized form 

 and is not very different from the ancient Devonian Crossopterygii, it seems to me 

 not improbable that the particulars of structure in which it resembles the admittedly 

 recent Teleostei are in both groups of a primitive nature. I do not pretend that upon 

 this point I feel very certain, but I think I have put forward some evidence in favour, 

 of the view I have taken. 



It is with reluctance that I publish a piece of work the material for which consisted 

 of a single specimen ; but as there seemed to be no prospect in the immediate future of 

 an abundant supply of the early stages in the development of Polypterus being obtained, 

 and as upon examination I found that there were points of considerable interest in 

 this small larva, it seemed only right that they should be known. I trust, however, 

 that when more material comes to hand it will be found that what has been seen in 

 this larva has been accurately described. 



