828 STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 



the Ganoids, the same arrangement of seminal ducts is found 

 as in Lepidostens, and it must therefore have been inherited from 

 an ancestor common to the two groups. 



If, therefore, the current statements about the generative 

 ducts of Ganoids are true, the males must have lost their vasa 

 efferentia, and the function of vas deferens must have been taken 

 by the homologue of the oviduct, presumably present in the 

 male. The Teleostei must, moreover, have sprung from Ganoidei 

 in which the vasa efferentia had become aborted. 



Considerable phylogenetic difficulties as to the relationships 

 of Ganoidei and Elasmobranchii are removed by the discovery 

 that Ganoids were originally provided with a system of vasa 

 efferentia like that of Elasmobranchii. 



THE ALIMENTARY CANAL AND ITS APPENDAGES. 



I. -Anatomy. 



Agassiz (No. 2) gives a short description with a figure of the 

 viscera of Lepidosteus as a whole. Van der Hceven has also 

 given a figure of them in his memoir on the air-bladder of this 

 form (No. 8), and Johannes Muller first detected the spiral valve 

 and gave a short account of it in his memoir (No. 13). Stan- 

 nius, again, makes several references to the viscera of Lepi- 

 dosteus in his anatomy of the Vertebrata, and throws some doubt 

 on Miiller's determination of the spiral valve. 



The following description refers to a female Lepidosteus of 

 IOO'5 centims. (Plate 40, fig. 66). 



With reference to the mouth and pharynx, we have nothing 

 special to remark. Immediately behind the pharynx there 

 comes an elongated tube, which is not divisible into stomach 

 and oesophagus, and may be called the stomach (j/.). It is about 

 44*6 centims. long, and gradually narrows from the middle to- 

 wards the hinder or pyloric extremity. It runs straight back- 

 wards for the greater part of its length, the last 3*8 centims., 

 however, taking a sudden bend forwards. For about half its 

 length the walls are thin, and the mucous membrane is smooth ; 



