416 , A. Aw. W. HUBRECHT. 
cesses of growth and organisation have been so hopelessly 
mixed up and misunderstood, we have to keep in view that 
an exaggerated importance has been ascribed to Amphioxus. 
I wish to insist upon this somewhat more fully. It is quite 
natural that, in the literature of the preceding century, a 
most particular and isolated position has been allotted to 
Amphioxus, as the very lowest fish-like being in the system 
of the Vertebrates, and we can neither wonder that in the 
second half of that century, in which the theory of evo- 
lution made its way, this position has considerably increased 
in importance, and that there arose a tendency to look 
upon Amphioxus as the real ancestral Vertebrate, out 
of which all the other fishes and Vertebrates had origi- 
nated. Haeckel has from the first accepted this view in 
his phylogenetic papers, and when then Kowalewsky had 
elucidated in such a masterly manner the ontogenesis of 
Amphioxus and of the Ascidians, the theory of the descent 
of the Vertebrates out of Invertebrates via the Ascidians and 
Amphioxus seemed to be definitely settled. This, however, 
was not the case, but then the beautiful and detailed re- 
searches of Hatschek on the development of the organs of 
Amphioxus have shown this animal to be such a perfect 
model of clear histogenesis in its early development, that it 
was only natural that all subsequent observers, who ‘occu- 
pied themselves with the embryonic development of higher 
Vertebrates, should have attempted to start from the data 
furnished by Amphioxus. 
anterior median portion of the pericardium is demonstrated in more than 
one preparation, In Sciurus it has not been followed out in full, but an 
early stage was noticed. Bats, too, seem promising in this respect. At all 
events, if this should be further confirmed, our whole interpretation of the 
vertebrate coelom would have to be recast. ‘That in such a case Balanoglossus 
among Invertebrates would have to be considered as an object of comparison 
would not be astonishing if we remember how a certain comparability between 
the branchial arrangement of Balanoglossus and Amphioxus has long been 
known. ‘The so-called notochord of Balanoglossus I would be inclined with 
Spengel to regard as a delusion. Gegenbaur in the latest edition of his 
comparative anatomy (Bd. 1, p. 185) has allotted to Rhabdopleura, which is 
related to Balanoglossus, a decided significance in the pedigree of Vertebrates, 
