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the affinity of the invertebrates with the vertebrates, it 
may be desirable to inquire what Dr. Donitz exactly means 
by affinity (Verwandtschaft); whether, perhaps, he was 
thinking of something like chemical affinity? But if he 
uses this expression in the ordinary sense in which it is daily 
used, it is difficult to understand how he supposes the verte- 
brate animals to have taken their origin. One certainly 
would not be indisposed to conceive of the vertebre as some- 
thing gradually brought about in the forefathers of the verte- 
brate animals, somewhat in the way in which we have above 
briefly endeavoured to explain. But then the forefathers of 
the vertebrate animals before they developed for themselves 
vertebre, necessarily must have been invertebrate; and yet 
we should account these invertebrate forefathers of the verte- 
brate as having “affinity” to them. It is, however, pos- 
sible that Dr. Donitz figures to himself the process of the 
origin of the vertebrata in some other way, more in the 
nature of a crystallisation ; so that suddenly, from an appro- 
priately large mass of blastema, the entire definitive organs 
came into existence as a kind of precipitate, or by successive 
Segregations around a centrum, which is perhaps to be dis- 
covered in the chorda. Then, in truth, we should have to 
understand by his expression “ affinity” (Verwandtschaft) 
a chemical affinity. 
There is only one more remark to make. Amphioxus de- 
velops notoriously in almost identically the same way as do 
the Ascidiz. Should then Amphioxus also be excluded from 
the ‘‘ Verwandtschaft’’ with vertebrata and the Petrony- 
zontes? Yet they, too, have no proper vertebre. Perhaps 
Dr. Donitz may succeed in a new essay in throwing some 
light on this matter. The gratitude of science will certainly 
not be withheld from him.—N. N. 
