510 PERCIVAL BAILEY 



versum, and Terry ('10) describes such a formation in Amia, as 

 well as folds which appear on the caudal wall of the velum. 

 The tela chorioidea diencephali itself forms a large thin-walled 

 dome with no plexus formation. There is a plexus in the roof 

 of the fourth ventricle. Lateral telencephalic choroid plexuses 

 according to Burckhardt ('94) are absent, but Hill ('94) writing 

 of Amia says: "It (the paraphysis) may be thought of as an iso- 

 lated portion of the roof of the fore-brain which owes its existence 

 to the formation of the folds marked Pl.chr. in figure 20, and 

 which are themselves the representatives of the choroid plexuses 

 of the lateral ventricles." 



Of the Urodeles, Burckhardt ('91) has described extensive 

 plexuses developing both from the tela chorioidea telencephali 

 medii and from the tela chorioidea diencephali in Ichthyophis. 

 Warren ('05) shows the enormous diencephalic plexus of Necturus 

 absorbing also the entire caudal wall of the velum transversum. 

 There is a plexus in the roof of the fourth ventricle. The lateral 

 telencephalic plexuses are present and arise from the base of the 

 median telencephalic plexus (plexus inferioris) as has been at- 

 tested by Mrs. Gage ('93), Studnicka ('93), Warren ('05) and 

 Burckhardt ('91). Burckhardt ('91) says of Ichthyophis: "Die 

 Plexus der Hirnhemispharen aber spalten sich je in zwei Stamme 

 von denen der eine sich gegen das Zwischenhirn ausstreckt, und 

 in der Folge zuerst sich in Zweige spaltet, indess der andere in 

 den Hemispharenventrikel eindringt und sich sodann in zwei 

 Zweige spaltet, einen nach rtickwarts umbiegenden, welcher den 

 Ventrikeltheil des Temporallappens und einen, welcher das 

 iibrige Vorderhirn versorgt." And Warren ('05) writes con- 

 cerning Necturus: "The telencephalic plexus develops from the 

 paraphysal arch " "The plexuses of the hemi- 

 spheres arise on either side from the origin of the telencephalic 

 plexus and pass into the lateral ventricles." 



Concerning the Chelonia, Humphrey ('94) shows a plexus aris- 

 ing from the tela chorioidea telencephali medii in Chelydra ser- 

 pentina, as does also C. L. Herrick ('91) in Cistudo. Warren 

 ('11) states that the plexus is not present in Chrysemys marginata 

 and with this statement my observations agree. The "two 



