250 
PROGRESS OF MICROSCOPICAL SCIENCE. 
cyclostomatous fishes the notochord, growing with the rest of the 
body into a highly developed form, acts as a substitute for the pillar 
of the bodies of the vertebrae, no vertebral bodies being developed ; 
but in cartilaginous and osseous fishes various gradations of carti- 
laginous and osseous structures come to surround the notochord and 
give rise to the simpler forms of vertebral bodies, which undergo 
more and more distinct development in the higher vertebrates. In 
all instances the substance forming the vertebral bodies is deposited 
on the surface of or outside the notochord and its sheath, so that this 
body remains for a time as a vestigial structure within the vertebral 
bodies of the higher animals. The observations of Kowalevsky with 
respect to the existence of a notochord in the ascidia, which have 
been confirmed by Kupfer and others, have produced a change little 
short of revolutionary in embryological and zoological views, leading 
as they do to the support of the hypothesis that the ascidia is an 
earlier stage in the phylogenetic history of the mammal and other 
vertebrates. The analogy between the amphioxus and ascidian larva 
is certainly most curious and striking as regards the relation of the 
notochord to other parts, and it is not difficult to conceive such a 
change in the form and position of the organs in their passage from 
the embryonic to the adult state as is not inconsistent with the 
supposition that the vertebrates and the ascidia may have had a 
common ancestral form. Kowalevsky’s discovery opens up at least an 
entirely new path of inquiry ; and we must be prepared to modify 
our views as to the entire separation of the vertebrates from the other- 
groups of animals, if we do not at once adopt the hypothesis that 
through the ascidian and other forms the origin of the vertebrates 
may be traced downwards in the series to the lower grades of animal 
organization. 
The Development of Batracliians icitliout Metamorphosis . — This fact, 
which was lately alleged to occur by a writer in a London journal, 
has produced a statement of some interest in the ‘ American Naturalist,’ 
August, 1877. The statement is made as follows by Mr. B.G. Wilder : — 
“ In ‘ Nature ’ for April 5, 1877, is an interesting article, author not 
stated, upon ‘ The Development of Batrachians without Metamor- 
phosis.’ On page 492 occurs the following passage : ‘ The young of 
Pina Americana (the Surinam toad) come forth from the eggs laid in 
the cells on their mother’s back, tailless and perfectly developed. In 
them, likewise, no one has yet detected branchiae.’ Two points here 
made arc not in accordance with the observations of the late Professor 
Jeffries Wyman, as recorded in the ‘ American Journal of Science and 
Arts,’ 1854, 2nd series, vol. xvii. pp. 369-374. Wyman states that 
the eggs are transferred by the male to the back of the female', which 
presents ‘ a uniform surface throughout ;’ ‘ their presence excites 
increased activity in the skin, it thickens, and is gradually built up 
around each egg, which it at length encloses in a well-defined pouch.’ 
On pages 370 and 371 he figures and describes the earlier embryos 
as having ‘ three branchial appendages on each side of the head. In 
a later stage the external branchiae had disappeared, but a small 
