130 IVAN E. WALLIN 



The minute structure of these buds is summed up in the 

 following : 



Was (Ion foineren Ban dieser Knospen anlangt, so gostattet mir die 

 mangdhaftc histologische Conservierung (Alkohol) vorlaufig nur 

 folgendc BernMTkungen zu machen: Von der kapsel dringen feine 

 Bindogcwcbsbiilkchcn in das Innere ein, welche ein spiirliches, reticu- 

 lumartiges Stutzgeriist fiir die zelligen Elemente biklen. Diese selbst 

 sind kloine Rundzellen von lymphoiden Aussehen, kaum wahrnehm- 

 barem Protopkisma, stark farbbarem Kern und Kerngeriist. Zwischen 

 densolben find en sich ausserdem grossere., blasse Kerne mit deutlicher 

 Kernmombran, und Kernkorperchen, welche dem Stiitzgewebe anzuge- 

 horen scheinen und rothe Blutkorperchen, von denen ich nicht sagen 

 kann, ob sie frei zwischen den lymphoiden Zellen liegen oder einge- 

 schlossen in Capillaren. 



Die tymphoiden Zellen sind wahrscheinlich Abkommlinge des Kie- 

 menepithels, wie ihr director tjbergang in das letztere vermuten lasst. 



In a subsequent paper Schaffer ('06) withdrew his previous 

 interpretation and said that he did not believe these structures 

 represent thymus anlagen. 



Giacomini ('00, 1 and 2) believed that 'Hhe lymphoid organ 

 in the basalar region of the gill lamellae (in ammocoetes) might 

 fulfill an analogous function to the thymus in the-fishes." 



Castellaneta ('13) describes the structures which Schaffer 

 found, but insists that these structures correspond to lymphoid 

 organs in general and suggests the name 'lymphoid formations' 

 for them. 



He further calls attention to the fact that on the one side 

 these lymphoid formations are in contact wdth the peribranchial 

 vessels and on the other with the epithelium of the branchial 

 sac. He does not consider these structures as thymus anlagen 

 insofar that there is not a reciprocal penetration of epithelial 

 and lymphatic elements which should occur in a thymus. Cas- 

 tellaneta calls attention to the abundance of lymphoid cells in 

 the general branchial region. He suggests that these special 

 lymphoid accumulations of Schaffer may represent a primitive 

 condition of the thymus in which the epithelium participates 

 only to the extent of attracting the lymphoid cells. 



These lymphocyte accumulations do not occur in the part of 

 the branchial cavity which would make them homologous with 



