ENLARGED PERICARDIUM IN LEBISTES EMBRYO 



199 



that thèse authors studied only the older stages (20-25th embryonic day) of 

 Lehistes reticulatus and that what Ryder and Turner thought to be an extension 

 of the yolk sac, is, in fact, the extended pericardium, The pericardial membranes 

 of Platypoecilus maculatus envelop the entire anterior portion of the embryo 

 during maximal development and form a neckstrap during régression (Tavolga, 

 1945; Tavolga and Rugh, 1947). The same situation is reported by thèse 

 authors for Xiphophorus helleri, in contrast to the observations by Turner (1940b). 

 The embryo of Heterandria formosa is shown by Fraser (1940) and Turner 

 (1940b) to have a pericardial sac expanding dorsally over the head and trunk to 

 the tailbud of the embryo. 



C) Anablepsidae (viviparous) 



Two species {Anableps anableps and A. dowei) were studied by Turner (1940a) 

 who cornes to the conclusion that the pericardium in this family achieves the 

 greatest enlargement. lt does not, however, grow over the head but in later 

 stages, after the yolk has been absorbed, surrounds as a thin cleft the whole 

 "belly sac" into which the viscera protrude. 



D) Goodeidae (viviparous) 



Ataenobius toweri, a primitive goodeid, displays a similar condition to 

 Fundulus heteroclitus described under A) above. The older spécimens of the 

 genus Goodea (three species), however, show a considerably more expanded 

 pericardial sac than found in Ataenobius toweri. Further species of this family 

 are described which show an evolutionary line in direction of a diminuation of the 

 yolk sac and a relative increase of the pericardial sac (Turner, 1940c). 



E) Yenynsiidae (viviparous) 



A hypertrophie pericardial sac is présent in Yenynsia lineata; it atrophies 

 with the receding yolk sac in the late embryonic stages (Turner, 1940d). 



One must take into considération that the embryos of the Goodeidae and 

 Yenynsiidae are not retained in the ovarian follicle until birth, as is the case in 

 the Poeciliidae and Anablepsidae but are liberated into the lumen of the ovary at 

 an early stage, where they continue development (Siccardi, 1940; Turner, 1947). 



When comparing the pericardium of the five cyprinodont families, it may be 

 concluded that the condition in the Cyprinodontidae foreshadows the formation 

 of pericardial headfolds, which become évident in the Poeciliidae, with Heterandria 

 formosa showing a maximal development. The Anablepsidae exhibit an even 

 greater expansion of the pericardium, which does, however, not resuit in a head- 



