204 



YVETTE W. KUNZ 



and embryonic tissue is "epithelio-chorial" as found in mammals with an extensive r 

 placenta (opposed to those with a massive placenta). Mammals with such an 

 extensive placenta (e.g. ruminants and pig) are characterized by the possession j 

 of a voluminous allantois. As this allantois contains very little urine, it is not 

 considered to be a storage place for excretory matter. Its main function is said 

 to press fetal against maternai circulation (Portmann, 1965). Similarly, the ! 

 function of the greatly enlarged urinary bladder in Lebistes reticulatus (and 

 Heterandria formosa as described by Fraser, 1940) may be to serve an intimate ! 

 contact between yolk sac (+ headfold) circulation and ovarian circulation during 

 the recession of the yolk material. 



The similarity can be drawn further when one considers the urinary bladder I 

 of teleosts to be of entodermal origin (Félix, 1898), as is the allantois of higher 

 vertebrates. According to Tavolga (1947) the bladder of Xiphophorus helleri 

 is formed from Kupfïer's vesicle, which itself is an outpushing of the postanal gut. \ 

 In other fish, however, the urinary bladder appears a long time after the Kupfïer's ! 

 vesicle has disappeared (e.g. in Serranus atrarius (Wilson, 1891), Esox lucius \ 

 (Gihr, 1957). Thus, there seems to exist not only an analogy but also a homology 

 between the allantois and the teleostean urinary bladder: both are of entodermal 

 origin; and moreover, in some mammals, the allantois is finally incorporated 

 into the urinary bladder. 



The phenomenon of the development of parallel structures in phylogenetically 

 unrelated groups is apparent, Lebistes reticulatus, a live-bearing teleost, having 

 developed "amniotic folds", an enlarged "allantois", and, perhaps, an "extensive 

 placenta". 



Thanks are due to: James Dunne for technical assistance, Hans Schaufelberger 

 and Matthew Foster for help with the illustrations and Volker Seelbach (Depart- 

 ment of Zoology, University of Basel) for letting me use his sectioned material 



SUMMARY 



1) The embryo of the viviparous teleost Lebistes reticulatus is characterized by 

 the development of a greatly increased pericardium, which is drawn over the 

 entire head. 



2) The outer wall of this headfold is vascularized ; the blood vessels are continuous 

 with the yolk sac circulation. 



3) The histological structure of the fully developed headfolds is established. 

 Their formation and régression are followed. 



4) Homology and analogy of the headfolds with the amniotic folds of the amniota 

 is discussed. 



