250 M.Van Beneden on the Physiology of the Simple Ascidians. 
but rather by an examination—mature, comparative, and based 
on the genesis of organization. It is four years since | studied _ 
with care the development of this product in the Aleyonella—nor 
has the delay in the publication of that work depended on me— 
and since then the facts in general have come to the support of 
my views. 
It has been said that reproduction by buds in some of the As- 
cidie@ is a very recent discovery ; and Milne Edwards assumes, for 
the basis of his classification, the twofold mode of reproduction 
by eggs and by buds. But in 1761 Bohadsch had observed the 
gemmiferous reproduction, and that even in a simple Ascidian, 
the A. intestinalis. Hence it was that, in the ‘ Encyclopédie Mé- 
thodique,’ Bruguiére wrote,—“ It is probable that, independently 
of their multiplication by eggs, they enjoy also a propagation 
by the integuments, according to the observations of Bohadsch 
and Miller.” 
The able Norwegian naturalist, Sars, has made some very cu- 
rious observations upon the mode of formation of the compound 
or aggregated Ascidiea, which perfectly explain the symmetrical 
arrangement of these little animals. Milne Edwards does not 
admit the plurality of germs to explain the aggregation, and he 
believes the formation by buds is sufficient to do so. Recently 
several important facts have appeared in support of the assertions 
of Sars, and it seems to me that doubt can no longer rest on the 
exactness of his observations. Some animals in their embryo con- 
dition, and before the adult form is reached, can divide themselves 
and disaggregate, by a natural fissiparous reproduction, into se- 
veral other individuals, which sometimes remain grouped together 
and constitute a ready-made colony (Ascidie composite), and 
sometimes they separate to live freely (Campanularie, Medusa, 
&c.). An animal of the lower classes can thus reproduce itself 
in its young age when it has still the embryo form: it dies in 
giving birth to another generation before having attained adult- 
ness, and that second generation has not passed through the 
same phases of the mother that gave birth to them. Be 
To explain the passage of the water from the respiratory ca- 
vity to the anal tube, openings or stigmata between the branchial 
vessels have been supposed necessary, but I rather coincide in 
the opinion of the naturalist who has lately denied the existence 
of these communications. I have always seen a thin membrane 
between the vessels; and the communication, in my opinion, is 
effected by an interruption of continuity between the parietes— 
which separate the respiratory cavity from the cloacum. 
Without having recourse to an alternating generation, as a 
learned Dane, Steenstrup, has lately advocated in a small but 
very remarkable book, it is easy, if we do not deceive ourselves, 
