1897.] Development of the Vertebral Column. 401 
other papers it is evident that he refers to a somewhat special- 
ized layer of cells belonging to the skeletogenous tissue. Ac- 
cording to Goette, the arches, upper and lower, are formed in 
the skeletogenous sheath outside of this perichordal sheath, 
and only later become applied to it. The primary vertebra 
thus consists of the arches, upper and lower, and the ring 
around the notochord. Furthermore, Goette contends that, 
primitively at least, two such vertebre belong to each somite. 
In few or no animals do we find both vertebre present in all 
their parts, but the author referred to finds vestiges of them in 
even the highest vertebrates. I cannot subscribe to these 
views. 
Without desiring to detract in the least from the merits of 
Goette’s embryological labors, I believe that I am not wrong 
in saying that the importance, even the existence, of this peri- 
chordal sheath has not been recognized by vertebrate embryo- 
logists. Most writers deny that the alleged sheath is anything 
more than a portion of the general skeletogenous layer and 
hold that it graduates into the latter. Hasse appears to come 
nearer than others in recognizing a special layer of the skele- 
togenous tissue ; but his “ innere Zellschicht” does not appear 
to correspond wholly with Goette’s perichordal sheath, since 
the former invests also the spinal cord. Furthermore, Hasse 
finds his layer of cells in Acipenser, to which genus Goette has 
denied the perichordal sheath. 
It is very apparent too that in one great group of vertebrates, 
the Elasmobranchs, Goette’s theory of the origin of the primary 
vertebral body has been demonstrated to be erroneous. Instead 
of there being, in these fishes, an “äussere Chordascheide” 
which has arisen as a distinctly specialized layer of the cells of 
the skeletogenous tissue, and which is a little later cut off from 
the less modified portions of this tissue by the elastica externa, 
it has been demonstrated by Klaatsch and Gadow and Abbott 
that the layer of cells called by Goette “ äussere Chordascheide ”, 
takes its origin from migrating cells which, starting from the 
bases of the arches, have pierced the elastica externa and made 
their way into the fibrous mass of the elastica interna. The 
“primary vertebral centrum” of the sharks must then be a 
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