434 



That its origin was in some way connected with the degeneration of 

 the branchial apparatus during the metamorphosis, was suggested by 

 HuscHKE (1826). He says: "Dieses dunkle Drüsenorgan ist demnach 

 nichts anderes, als die verschmolzenen, drüsig gewordenen Kiemen- 

 fasern." Fleischl (1868) designated it as "sogenannte Schilddrüse". 

 ToLDT (1868) recognized its lymphoid structure and characterized it as 

 "fälschlich sogenannte Glandula thyreoidea", believing that a true thyroid 

 gland did not exist in the frog. W. Müller (1871) described the deve- 

 lopment of the true thyroid gland of the frog, and Babes (1881) 

 demonstrated its existence in the adult. It remained for Maurer to 

 bring order out of the confusion that existed in our knowledge of 

 the various glands and gland-like structures derived from the gill- 

 clefts of the Amphibia. Mayer (1888) suggested the name "Pseudo- 

 thyreoidea" for the so-called thyroid, but disclaimed any exact know- 

 ledge of its derivation. 



Simon (1844) described and figured as the thymus gland of the 

 frog an unpaired structure lying anterior to the base of the peri- 

 cardium. This body seems to have escaped the notice of subsequent 

 observers, until Gaupp rediscovered it and named it the Corpus 

 praepericardiale, later designating it as C. propericardiale. 



According to Maurer the ventral Kiemenrest developes from the 

 epithelium of the ventral part of the branchial chamber at the time 

 of the metamorphosis. He says : "Sie entstehen durch Wucherung des 

 vordersten ventralen Endes der Kiemenhöhle, und zwar kommt es 

 dabei zur Bildung eines gemischten Gewebes, in welchem lymphoide 

 Rundzellen am zahlreichsten vorhanden sind." In tracing in Ran a 

 fuse a the development of the Corpus propericardiale, my 

 attention was early called to the similarity in structure of the latter 

 body to the ventral Kiemenrest. Careful investigation soon led me 

 to the conclusion that neither body has any genetic relationship with 

 remnants of the branchial apparatus. Both originate in a similar way 

 and at the same time, as will be subsequently shown. From this 

 point on in this paper the "ventraler Kiemeurest" of Maurer will be 

 designated as "pseudothyroid" (S. Mayer). 



Maurer describes and figures in Ran a esculenta at the close 

 of the larval period a solid epithelial knot situated on the anterior 

 median wall of the outer branchial cavity. This he considers the 

 beginning of the ventral Kiemenrest. In Rana fusca I find no such 

 similarly situated formation at any period. On the ventral floor of 

 the branchial chamber there is constantly present during the late 

 larval period and the early metamorphosis a lymphoid knot (Fig. 6 Im), 

 but this has not the least relation to Kiemenreste. In R. fusca I 



