ASCIDIIDiE. 
179 
as soon as batched from the egg, shows all the essential 
features of the full-grown stage, to which the development pro- 
gresses within the egg. He also remarks that the same animal 
produces either single isolated eggs or a sort of spawn, between 
the individual eggs of which and the isolated eggs no difference 
can be observed. The author thinks this simple development 
may be regarded as the typical one of the Tunicataj and that in 
the Ascidia it begins much in the same manner, but becomes 
complicated by the known peculiarities of the larva, which put 
it in relation with the Vertebrata — the latter diverging course of 
development, however, being abruptly stopped, and the animal 
falling back to the inferior organization, which ivS never exceeded 
by either of the above-mentioned species of Molgula. Arch, 
mikr. Anat. viii. pp. 364-384, pi. 17. figs. 1-8. 
The same author, discussing in detail the nervous system of the 
larva of Ascidia\-ium] meniula (Miill.), describes a light-break- 
ing apparatus, and an otolite supported by cilia, in the anterior 
cavity, which he calls the cerebral vesicle (Hirnblase). He com- 
pares the fold of the inner membrane of this cavity, which sur- 
rounds and fixes the light-breaking body, with the zonula zinni 
in the human eye, and describes equidistant bundles of what he 
calls spinal nerves along the nervous trunk running above the 
chord in the tail of the larva. These nerves, however, can only 
be seen distinctly for a few seconds after the death of the ani- 
mal. Ibid, pp. 385-396, pi. 17. figs. 9 & 10 ; the optic apparatus, 
fig. 10, /; the otolite and its cilia, fig. 10, c and e; the spinal 
nerves, fig. 9, s, 
hi. Metsciinikoff, having repeated his researches concerning 
the first development of the Ascidia, agrees with Kowalcwsky 
that the first germinal layer (erstes Keimblatt) shares in the 
formation of the nervous system, and that the horseshoe-shaped 
organ is the matrix of the cellular string of the tail ; but he 
maintains that the second or inferior germinal layer (zweites 
Keimblatt) also shares in such formation, and he proves it from 
the figures drawn by Kowalewsky himself. The cells of the 
tunie come directly from the protoplasm of the egg-cell (this 
is also the opinion of C. Kupffer). All this can be observed very 
distinctly only in species with pellucid eggs, as Phallusia mammiU 
lata (Sav.) ; and the contradictory results of the researches of 
Kupffer, Ganin, and Donitz are due to their having been ob- 
tained from less favourable species. Z. wiss. Zool. xxii. pp. 
339-347. ^ 
A. Giard reviews the recent publications on the structure of 
Ascidian larvae and their relation to the type of the Verte- 
brates. Although differing in some points from the view^s 
brought forward by Donitz (see Zool. Rec. vii. p. 184), becomes 
to the conclusion that the resemblance of tbe chord in the tail 
with that of the Vertebrate is only an homology by adaptation 
