ENLARGED PERICARDIUM IN LEBISTES EMBRYO 



203 



gaseous exchange. Somewhat later (about 25th embryonic day) the mouth 

 movements begin and perivitelline fluid is drawn into the pharyngeal cavity. 

 Two to three days later opercular movement starts which results in a dorsal 

 ' splitting of the vascularized neckstrap. Respiration by the gills is now in progress 

 as the remnants of the neckstrap are rapidly absorbed. 



iB) Accessory nutritive function 



Teleostean yolk sac vessels are the means by which yolk products are trans- 

 ported to the embryo. In the viviparous poeciliids, the vitelline circulation is in 

 close contact with the maternai ovarian circulation. It is suggested, therefore, 

 by différent authors that the embryos obtain additional nutrients from the mother 

 (Bailey, 1933, Turner, 1940a-d and 1947, Scrimshaw, 1944 and 1945, Trinkaus 

 and Drake, 1952, Rosenthal, 1953, Tavolga and Rugh, 1947, Tavolga, 1949). 

 Apart from the findings for Heterandria formosa (Scrimshaw, 1944), there seems 

 to be no évidence, in Lebistes reticulatus and other poeciliids, that yolk sac circula- 

 tion with its extension into the headfolds are of a placental nature. 



C) Accessory excretory function 



It has been suggested by Tavolga and Rugh (1947) that the extended peri- 

 cardial sac in Platypoecilus maculatus is also a means of nitrogenous disposai. 

 As mentioned earlier, Lebistes reticulatus is characterized by a urinary bladder 

 which increases greatly in size during embryonic development (Kunz, 1963). 

 The increase in bladder size in this species occurs concomitantly with an accéléra- 

 tion in the utilization of yolk. So it may be the function of the greatly enlarged 

 bladder to store waste products which can no longer be handled by the yolk sac 

 circulation, having lost its extension into the headfolds. To prove this view the 

 chemical nature of the contents of the urinary bladder must be known. 



On the bâ^sis of the data given in the publications referred to above and on 

 the basis of présent observations no conclusion can be drawn as to whether the 

 functions of the vascularized headfolds are nutritive, excretory or respiratory, or 

 indeed a combination of two or more of thèse. Equally, it is not known if the 

 greatly enlarged bladder stores waste products. It is désirable, therefore, to leave 

 aside this controversy and discuss in the following section the relationship 

 between headfolds and enlarged urinary bladder and its probable significance. 



5) Significance of ectodermal and pericardial headfolds 

 related to development of enlarged urinary bladder 



It has been shown that the circulation of the pericardial sac in Lebistes 

 reticulatus is an extension of the vitelline circulation and that both are in close 

 contact with the maternai ovarian circulation. The contact between maternai 



