The Development of the Cartilaginous Skull ete. in Necturus. 445 
Ras ('89, page 228) supports his theory. Rast tells us, »es ent- 
wickeln sich bei allen (!) Wirbelthieren die Urwirbel der Reihe nach 
von vorn nach hinten, so dass also der vorderste Urwirbel zugleich 
der älteste ist. Dieser vorderste Urwirbel ist aber identisch mit 
dem fünften (!) Kopfsomit van Wısne’s, dem ersten distalen (i. e. 
postotic) Somite. Auch die weitere Entwicklung der fünf distalen 
Kopfsomite ist genau dieselbe wie die der nächstfolgenden Urwirbel 
des Rumpfes (!)«. 
Although the chick is a familiar object for the investigation of 
simple phenomena of development, at the time when I studied (’89) 
the succession in which the protovertebrae arise, there were, as far 
as I know, but three published studies describing their order of 
origin (v. BAER ’28—’37, His ’68, Kuprrer and BENECKE ’79), and 
none of these studies claimed that the most anterior protovertebra 
is the first to form. I should doubt whether the order in which the 
protovertebrae arise had been investigated in all Vertebrates, were 
is not for the authoritative statement of a man (RaBL’89, page 115) 
who warns us that, »der Forscher soll die Wahrheit iiber Alles 
halten; er darf sie nie der Klarheit zum Cpfer bringen: denn was 
heute nicht ganz klar ist, kann es morgen werden; aber was heute 
eine Lüge ist, bleibt in alle Ewigkeit eine Lüge.« 
v. WIJHE (82) says that he believes that the first somites that 
appear in the Selachii are those of the region corresponding to the 
neck of higher Vertebrates, and HorrmMann (97) confirms this belief, 
adding that the order of development of the motor nerves, like that 
of the protovertebrae, is in two directions, thus bringing further evi- 
dence against the assumption that successive development in one 
direction is a prerequisite of homodynamy. Kerrpen (95) tells us 
that the first formed protovertebra in the Mammalia is not the 
most anterior. I also found (’89), and my observation has since been 
confirmed by GoronowirscH (93), that in the chick, the first divi- 
sion in the axial mesoderm falls between the second and third proto- 
vertebrae, and that two protovertebrae are slowly cut off anterior 
to this primary division of the mesoderm, while the formation of 
protovertebrae in a posterior direction takes place more rapidly. 
The protovertebra first formed in the chick is consequently the third 
in position. 
RABL moreover says, as above quoted, that the first protovertebra 
corresponds to v. WisuE’s fifth somite, and that this protovertebra 
with the four following (i. e. the five distal head somites) develops 
