ORIGIN AND STRUCTURE OF THE HEAD 123 



been made to derive the brain of Craniates and its main 

 peculiarities from the brain vesicle of Amphioxus. One of 

 the best known is that of V. KUPFFER (1906, 11. 3, p. 13) 

 who homologizes especially the archencephalon to the 

 brain vesicle of Amphioxus, while the deuterencephalon 

 is compared with the anterior end of the neural tube. The 

 tuberculum posterius, a thickening of the floor of the Craniate 

 brain over the plica ventralis which indicates the limit of 

 arch- and deuterencephalon, is found again by V. KUPFFER 

 as a group of ciliated cells in the floor of the brain vesicle 

 of Amphioxus. These cells were first described by BOEKE 

 (1902, p. 411) and termed by him the "infundibular organ". In 

 front of it KUPFFER (1. c. fig. 5, p. 7) even thinks he finds an 

 infundibular depression comparable to the infundibulum of 

 Craniates. BOEKE (1908), however, afterwards showed that 

 such a depression does not exist. He sees the homologon of the 

 infundibular organ in the sensory epithelium of the saccus 

 vasculosus of fishes. A comparison of what WiEDERSHElM 

 says in the successive editions of his Comparative Anatomy 

 about the homology of the brain of Craniates and the 

 brain vesicle of Amphioxus shows clearfy how opinions 

 on this subject have altered. In the first edition (1883, p. 

 275) we read ; "Durch die Lage und Ausdehnung der Chorda 

 dorsalis im Schadelgrund kann man a priori einen 

 praechordalen und chordalen Hirnabschnitt 

 unterscheiden. Jener sowie auch die zugehorige Schadelregion 

 ist als ein spaterer Erwerb und daher nicht einfach als 

 transformirtes Ruckenmark zu betrachten (GeGENBAUR). 

 Daraus ergeben sich wichtige Consequenzen furdasGehirn 

 von Amphioxus, wo ein praevertebraler Kopfabschnitt gar 

 nicht zur Entwickelung kommt", and p. 282-283: "Da die 

 Chorda des Amphioxus sich bis zum vordersten Leibesende 

 erstreckt, so kann auch, wie wir schon oben hervorgehoben 

 haben, der dariiber liegende Hirntheil nur dem chordalen 

 Gehirnabschnitt der ubrigen Vertebraten .... entsprechen." 

 It is especially the comparison of the neuropore in 

 Craniates and Amphioxus, one of the main arguments also 

 of V. KUPFFER, which in the 2nd and 3rd edition induces 

 WiEDERSHElM to homologize the brain vesicle of the latter 

 to the fore-, perhaps also to the raid-brain of Craniates, 

 while in later editions he leaves the question undecided, 

 saying: "Welchen Abschnitten des Gehirnes der Cranioten 

 das Amphioxushirn entspricht, lasst sich nicht mit Sicherheit 



