THE ADHESIVE ORGANS OF AMIA. 1 43 



they are modified sense buds but this is certainly not the case in 

 Amia. But the fact that in Acipenser the adhesive organs 

 become tactile organs, put with von Kupfer's statement that the 

 adhesive organs and the hypophysis have a common anlage may 

 suggest some remote connection with the nervous system. 



As to the phylogeny or meaning of these organs facts are too 

 few to form a basis for any very extensive or certain conclusions. 

 In the various species of ganoids they may have a common 

 function; whether they have a common origin is doubtful. They 

 do not have a common fate. In Amia they disappear entirely. 

 In Lepidosteits they leave only a useless rudiment. In Acipenser 

 they become the barbels. This last fact may furnish a clue to 

 the origin of the barbels in the teleosts as suggested long ago by 

 Balfour. The adhesive organs of ganoids — if we may base our 

 conclusions on their development in Amia — are not homol- 

 ogous with the sucking disks of the amphibia or the teleosts. 

 So far as we can see now these organs were developed independ- 

 ently in different groups of animals. But living forms of ganoids 

 are so few and so aberrant that any conclusions based on the 

 study of these forms alone will probably be only tentative. 



Summary. 



The development of the adhesive organs in Amia begins about 

 70 hours after fertilization when the embryo extends over about 

 160 degrees of the circumference of the egg. 



They appear as paired thickenings of the dorso-lateral portion 

 of the anterior end of the foregut. They are therefore ento- 

 dermal in origin. 



They grow out as paired diverticula of the foregut, break 

 through the epidermis, become greatly subdivided and form a 

 horseshoe-shaped structure at the end of the snout. 



Histologically they consist of high columnar epithelial cells. 

 These cells are at first heavily laden with yolk granules espe- 

 cially at their base. They contain a reticulum coarser at the 

 base. Metabolic activity is at first greater at the basal end of 

 the cells but later it is greater at the distal end. 



The function of these cells is undoubtedly to secrete a mucous 

 substance by means of which the young fishes attach themselves 



