QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 79 
mouth) subsequently breaking through and completing the 
*‘ oastrula,” which then becomes fixed by attachment of the 
aboral pole. Metschnikoff did not find the endoderm to be 
ciliated in the species studied by him, after fixation, whereas 
Haeckel did in the cases studied by him. 
Carter, in the Annals and Mag. Nat. Hist., Nov. and Dec., 
1874, gives an account of observations on the development 
of Siliceous Sponges, which will be found of interest in con- 
nection with the above. 
Hydrozoa. — Metschnikoff describes the development of 
many Meduse and Siphonophora in a paper in Koll. u. Sieb. 
Zeitschrift, part i, 1874, illustrated with eleven folding 
plates. He again finds occasion to differ very largely from 
Haeckel, whose prize memoir on the development of the 
Siphonophora is the most complete account at present pub- 
lished of this matter. The most interesting part of Metschni- 
koff’s memoir is that in which he discusses some parts of 
the Gastrea-theory, and in particular expounds his views as 
to the nature of the coelom or body-cavity and the relation- 
ship of the Echinodermata and Celenterata. He dissents 
altogether from Haeckel’s view, adopted by Gegenbaur, that 
the Echinoderms are to be regarded as radial colonies of 
worm-like individuals arranged around a common stomach. 
Metschnikoff draws attention to the confirmation which he 
has previously given to Alex. Agassiz’s observation, to the 
effect that the ambulacral system is an outgrowth of the 
alimentary canal of the larva, and further, that the whole 
peritoneal system of the Echinoderm is of the same nature 
and quite distinct from the body-cavity of the larva. In this 
case Metschnikoff contends that the cavities of the Echino- 
derm’s body, outside the alimentary canal, are directly 
comparable to the gastrovascular system of Rhizostoma and 
the Ctenophora. In Bipinnaria the cavities in question com- 
municate provisionally with the gastric cavity which in the larva 
takes its rise by invagination—a condition which in the Celen- 
terata exists throughout life. The two openings of the canal 
system of Ctenophora Metschnikoff regards as corresponding 
to the pore of the ambulacral system, which is double in 
some Kchinoderm larve. Further, he will not allow that in 
Coelenterata there is no representative of a true body cavity, 
that is, of a cavity arising between the body-wall and 
intestinal wall, independent of all communication with the 
alimentary cavity. ‘This he finds in the space occupied by 
the jelly-mass in Medusze and Ctenophora, in which so-called 
‘‘mucus-tissue ” is often developed. ‘This corresponds with 
the true body-cavity of the Echinoderm-larya, which is filled 
