90 
Now, proceeding from the actually observed form //, one might 
cast a look into a comparatively ancient period of the history of 
the vertebral column. 
If in analogy of the formulas //f to // one were to construe 
succeeding formulas to the formula //, the first in succession would 
be a formula, denoting the 31% vertebra as a sacrocaudal vertebra: Ze. 
The latter must be preceded by a form of the vertebral column 
in which the 31st vertebra is the last and moreover the sixth sacral 
vertebra: /d. Here the 21st vertebra must be the first lumbal vertebra 
as in the formulas //c to Ze. 
Inasmuch as now a first lumbal vertebra is developed from a 
last dorsal vertebra, after it has passed through the stage of a 
dorsolumbal vertebra, the next following more primitive form must 
possess the 21 vertebra as dorsolumbal vertebra, as is indicated in 
the formula Jc. 
And this must have been developed from a form in which the 
21st vertebra is the last and moreover the 14!!! dorsal vertebra, which 
characterizes the formula ZD. In this formula the 26‘ vertebra is the 
first of a sacrum, consisting of 6 vertebrae. A first sacral vertebra, 
however, develops from a last lumbal vertebra, after it has been 
lumbosacral vertebra. 
Consequently we can imagine a formula, showing the 26 vertebra 
as lumbosacral vertebra, in which at the same time 14 dorsal vertebrae 
and 4 lumbal vertebrae are extant, besides a sacrum, consisting of 
five vertebrae. This is indicated in the formula /a. 
And if now we go one step more backward, then it must be 
possible to find a vertebral column in which the 26th vertebra is 
the last and moreover the 5 lumbal vertebra, then a sacrum of 5 
vertebrae must follow and 4 caudal vertebrae must succeed to this, 
the last of which is the 35 vertebra of the series. This gives the 
formula /. 
With regard to the formulas /e to /a I must admit, that they 
are purely hypothetical; with regard to formula J, however, I 
should wish to cite an observation, answering almost entirely to this 
formula. 
First I must, however, briefly fix the attention to a peculiarity, 
occurring in vertebral columns standing on the. ten stages mentioned. 
If a special stage is represented by more than one specimen we 
see in these specimens differences that have a morphological signification. 
As an example I wish to cite the stage ///a, which is represented 
by three vertebral columns. 
One glance at the illustrations is sufficient to see that these three 
