142 A. C. EYCLESHYMER AND J. M. WILSON. 



to the germ layer from which these organs are formed. But we 

 cannot agree with her statement that the organ consists at first 

 of a single diverticulum which subsequently divides into two. 

 We find the anlagen of the adhesive organs in paired thickenings 

 of the dorso-lateral portion of the anterior extremity of the fore- 

 gut (Fig. 3). As soon as these become recognizable as diver- 

 ticula there are plainly two of them. 



As to their method of disappearance we are unable to find 

 anything which indicates an infiltration of leucocytes or phago- 

 cytosis. On the other hand everything suggests an autogenous 

 degeneration. 



It has been shown beyond question that in Amia the adhesive 

 organs are developed from the entoderm. But in the other 

 ganoids, Acipenser and Lepidosteas — while the proof is not con- 

 clusive — the balance of authority favors the view that they are 

 formed from the ectoderm. A priori it does not seem probable 

 that homologous organs would be formed from different germ 

 layers. But what proof have we that these organs are homo- 

 logous ? Sucking disks are formed in many species of animals 

 in widely different groups. Generally they are temporary larval 

 organs, and it can be easity shown that they are not in all cases 

 homologous organs. In those amphibia which have sucking 

 disks these organs are undoubtedly ectodermal in origin. In the 

 teleost Eclieneis {Remord) the great sucking disk — an adult 

 organ in this case — is developed from the anterior end of the 

 dorsal fin. Ascidians also develop sucking disks ; they too are 

 ectodermal. 



As to the function of these organs all authorities seem to be 

 agreed. Their function is to attach the young fish to some 

 solid object. As a rule the organ is well developed when the 

 fish is hatched and the little fish attaches itself immediately. 

 This is true at least of Lepidosteus and Amia. In Amia the organ 

 serves to keep the young fish attached for about a week ; in Lepi- 

 dosteus about two weeks. 



Whether the organ has now or ever has had any other func- 

 tion has not been shown. It has been suggested that they may 

 serve to convey some sort of nutriment to the digestive tract but 

 we have found no proof of this. It has also been suggested that 



