THE ADHESIVE ORGANS OF AMIA. 1 39 



lysis and the cells are absorbed. The ectodermal cells forming 

 the organs, as shown in the figure, likewise are much swollen, 

 their outlines are indistinct and connective tissue grows in among 

 them. Their nuclei are less readily stained with basic stains. 

 The cytoplasm becomes vacuolated and granular; all of which 

 points to albuminoid degeneration. 



Historical and Critical. 



The first author to treat of the development of the adhesive 

 organ of any ganoid was Alexander Agassiz ('78) in his paper 

 on Lepidostens . But his observations were limited to the period 

 after hatching. At this time the development of the organ is 

 nearly completed and his descriptions therefore refer mainly to its 

 function and its degeneration and disappearance. He describes 

 the "huge mouth cavity" of the newly hatched Lepidosteits 

 " surmounted by a hoof-shaped depression edged with a row of 

 protuberances acting as suckers " and compares it with the mouth 

 of the cyclostomes. The moment the little fish is hatched it at- 

 taches itself firmly to the side of the dish and there remains 

 hanging immovable. Three days after hatching the disk becomes 

 more prominent, "the individual suckers projecting frequently 

 beyond the general outline of the edge of the suckers." As the 

 snout lengthens the suckers become concentrated and the size of the 

 terminal disk is reduced. When the fish is three weeks old "the 

 sucking snout is now reduced to a swelling of the extremity or 

 the elongated upper jaw." Later the disk is reduced to a single 

 row of small suckers and finally it becomes the fleshy globular 

 termination of the upper jaw of the adult. 



Balfour and Parker ('82) continued the work on Lepidosteits, 

 working on material furnished by Agassiz. They state that the 

 disk is formed two or three days before hatching but give no 

 details. They give two figures showing something of its histo- 

 logical structure and add : " The result of our examination has 

 been to show that the disk is provided with a series of papillae 

 often exhibiting a bilateral arrangement. The papillae are mainly 

 constituted of highly modified cells of the mucous [inner] layer 

 of the epidermis [epiblast ?]. These cells have the form of elon- 

 gated columns, the nucleus being placed at the base and the main 



