the hyobranchial skeleton develops in tadpoles has no homologue among the ancestors of the 

 as in urodelan larvae. The single new element tailless amphibians. The remaining elements of 

 is copula I. Shortly after the arches are laid the hyobranchial skeleton in the larvae of Anura 

 down the formation of the long convoluted in- are changed because of a deviation evolved by 

 testine begins. The latter literally forces the means of positive anabolism. The transport of 

 heart into the region of the hyobranchial appa- dispersed food material required an increase in 

 ratus, changing its configuration and the entire the amount of water circulated through the oro- 

 course of its further development. The hyo- pharyngeal cavity. With this a proportional in- 

 branchial skeleton moves somewhat rostrally, crease of the medial parts of the ceratohyal ia 

 consequently the hyoid comes in contact with occurred, leading to the restructuring of the 

 the quadrate cartilages. At this spot the , ceratobranch ial ia of the gill chambers and the 

 quadrate articulation develops. Copula II fusion of hypobranch i al i a into a broad disk, 

 (we succeeded in showing the homologue of the Among the forms investigated, the tadpoles of 

 copula in urodelan larvae) having lost the possi- Di scogloss i dae and Pelobatidae are more primitive 

 bility for growing caudally remains arrested as in several structures of the hyobranchial system 

 a short cartilage throughout the entire larval than are the tadpoles of the Ranidae, Bufonidae 

 life of Anura, cf a size equivalent to that and Hylidae. Maximal spreading of the hyoid and 

 seen in the early stages of larval development the gill chambers is noted in the tadpoles of X, 

 in the Urodela. laevisi the latter characteristically feed on 



decaying matter and phytoplankton and hence re- 



Hypobranchial ia I and II approach one quire increased amounts of water to pass through 



another and fuse. In the larvae of Phanero- the oro-pharyngeal tract, 

 glossa the mouth remains ventral until meta- 

 morphosis. Consequently the arches of the The transformation of the hyobranchial skele- 



hyobranchial skeleton retain their initial ton is paralleled by the transformation of its 



transverse position. The change of conf igura- musculature. The M. cera tohyo i deus exterior , which 



tion and topography of the hyobranchial skele- lowers the cera tobranch ial ia in the larvae of 



ton observed in the anuran larvae must then have Urodela, disappears. New muscles develop, namely 



arisen as a result of a deviation from the the Mm. orbita a *d suspenseric hyoidea. The Ma. 



course of development characteristic for the levatores arcuum branchialium expand and in the" 



urodelan larvae. This deviation apparently re- tadpoles of X. laevis may even fuse into a single 



suits from interactions in forming the intestine mu scle layer. The Mm. constr ictores branchial es 



and the heart and the lack of any tendency by develop in anuran larvae as a result of the 



the mouth to translocate. In tadpoles the development of the concealed gills and the re- 



hyobranchial apparatus then acts differently as duction of the gill flaps (which in the larvae of 



the plane of its oscillation changes (since the Urodela close the gill slits during the intake of 



arches lie in a transverse position rotation of water into the 0P0 _ phaPyngeal tract cavity). The 



the hyoid in the sagittal plane cannot lower the pre sence of these muscles in the tadpoles of X. 



floor of the oro-pharyngeal cavity). It must be laevis attests to the fact that gill breathing has 



emphasized that this deviation arose by means of in this specjes d i sa p pea red for a second time, 



a changed construction i n correlated mutual re- The development of Mm. constr ictores branchiales . 



lationships (co-adaptation) of the hyobranchial which close the giu slit , § thfi s , charac - 



apparatus with the orqans surroundinq it. The *«.«.:=+:.. xk* * . ,4 : * ■ _ a a -x- i- x ., 



, r , , . , ., . , , . , . , , tenstic that conditioned the unification of the 



transformation of the hyobranchial apparatus took functions of breathing and food transport in the 



place not as a result of direct adaptation to the hyobranch ial appaPa tus of tadpoles. 



changed character of the food but indirectly, be- 



cause of a change in other organs. The muscles which participate in the raising 



,...,. ., . _, , , °f the floor of the oro-pharyngeal .cavi ty have 



The deviation described above determined all l... -,,k :.»i-j *„ -..„4 _1 i ± x i • 



, , . , .. , . , oeen subjected to just as great a transformation, 



further evolution of the hyobranchial apparatus. tl. u ;„t„k „j_. j. • i, 



, . . . .. . J . . v . ihe M. interhyo ideus posterior is well expressed 



Hvpohval ia noted in the beqinninq stages of ;_ tko i._,,,_ „x p-i„k«*-j u i k i • 



, ' v ' , ,.,,.,.,, . . ' n the larvae ot relobatidae, but absent in a 



development of the hyoid under the edge by the co,.;^ «-f i n .,»^+ ; „=, *„,j x„ .... Tk u • * ■_ ■ j 



, \ . . i '., ,_.._■ •, \ j series ot investigated forms. The M. i nterhvo i deus 



ceratohyal i a (as in the hvnobiid larvaej do not ,„<„_;„_ • ,. ,,-j_ iu i x n — j — ; . , 



—~ — ^~. — . v .,. , { , , . , anterior is wide in the larvae of Urodela: but 



change their position, but spread out and fuse .„„„„„ __ , , ■ .. ... ., 



, ? ,, . .... appears as a narrow strip in connection with the 



forming the pars reun i ens , which is not cart i - *._.„„..«_„• i „ x • x il l. -j • i l -i 



3 , ,*— ' . ' , . , . ,, transverse location of the hyoid in the larvae 



laginous but remains prochondnal for the en- x ,, ,, . ',. , . v ,-_.._ 



..,,,.,« ., 0+ al l the Phaneroqlossa. In the larvae of X.. laev is 



tire larval life. Oonsequently the pars -i ■ ___;_ k _ji tl. u j-k •> 



M , ' - r . , . .. it is again broad. The M. i ntermand i bular i s 



i ens (which arises as the result of deviati 



anter i or and M. gen i ohyo i deus which determine the 



in the development of hvpohval ia particular to ,4._._x: x i? Z -a T^ i • i. L i 



,, , / ,, , , \ J y ,' :— y . . ,. protraction of the hyoid and copula in the larvae 



the larvae of Urodela; is the homologue of these , .. . . ' , ,, . 



. , .. . . ' . . . . . , a j . t of Urodela are in tadpoles kept from this 



elements of the hyobranchial skeletons and is not . r , . , r 



. , . ,. ,' . ., ., x ■ „i- , function by the hyobranchial apparatus, and in- 



basal as believed by the maiority of investiga- , ,..,... . . 



. T . • t .• stead participate in the mechanism of action for 



tors. The pars reun i ens serves as an elastic ,. r •" , , ' , 



r , 77 . . . . , ,. the lip cartilaqe. The Mm. subarcuales obi. 

 connection between the ceratohyal ia when these . ,,, . _. , . . am.- 



move in the transversal plane. Copula I which * nd ''' ^ re '"dependent ,n the larvae of Urodela. 

 possesses the most primitive construction in n tad P°lf («'th the exception of those fiU) 



pelobatid tadpoles (it is lacking in the tad- they are fused into a single muscle and in X. 



poles of Xenopus laevis ) arose in the process of f? evis the y furthermore lose their connection with 



evolution of the larvae of Anura of arcolaxis and the co P ula - Th * evolutionary transformations of 



