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184 MOLLUSCOIDA.
dorsal and ventral side of these animals, in the same manner as
the late Keferstein.
A short abstract of Kowalewsky's and Kupffer's researches concerning the
embryology of Ascidia; is to be found in Journ. Micr. Sc. 1870, pp. 59-69
and 299.
Dr. W. DONITZ opposes these views. He states, from observations
on Clavellina lepadiformis (Miill.), made by him at
Naples, that the cleaving of the yelk and the formation of
a yelk-membrane is here as usual, that the intestine is not
formed by any invagination, that the central nervous system, as
described by Kowalewsky, is not found in the larvae of Clavellina,
and concludes that the string of cells, intermixed with vacuoles,
in the axis of the tail of those larvae is only apparently similar
to the chorda of a vertebrate, but really quite different,—these
cells being arranged concentrically, and not in bilateral order,
and nothing like a vertebra being associated with them; he
thinks it even very doubtful if the adjoining cells can be regarded
as muscular cells. SB. nat. Fr. 1870, pp. 47-51; also in Arch.
Anat. u. Phys. pp. 161-164.
M. GANIN, from his observations on the development of the
compound Ascidiae (see below), comes to the conclusion that the
nervous system of the embryo is, in its development, in its form,
in its structure, and in its local relations to the other organs,
more similar to the nervous system of the embryo of the Vertebrata
than to that of any other embryo or full-grown animal.
The ciliated pit in the Ascidia? is to be compared to the nasal
organ of Amphioxus. He coincides, therefore, with Kowalewsky
[and Kupffer] as to the affinity of the Ascidia? in their embryonic
stage with the Vertebrata, and refutes the objections made by
Mecznikow (Zool. Rec. vi. p. 591). Z. wiss. Zool. xx. pp. 513,
517.
LACAZE-DUTHIERS, studying the development of various genera
of Ascidians by means of artificial fecundation, observed the very
strange fact that the embryo of what he believes to be Molgula
tubulosa is widely different from that of others, being an unformed
mass, with slow amoeboid motion. C. R. June 1870,
and R. Z. 1870, pp. 206-209; translated Ann. N. H. (4) vi.
pp. 109-111.
A. HANCOCK points out that a tadpole-like larva, like that of
other Ascidia?, has also been observed by Van Beneden in a real
Molgula, ampulloidea (Beneden), and by himself inM. complanata,
sp. n.; and he suggests that the animal observed by Lacaze-
Duthiers was not a true Molgula, but Eugyra arenosa, Aid. and
Hauc. His observation, however, is not the less interesting on
that account. Ann. N. II. (!) vi. pp. 353-355.
Ascidia plana, aldcvi, rubrotincta, rubicunda, robusta, mollis, crassa, inornata,