1200 The American Naturalist. [December, 
ZOOLOGY. 
Fresh-Water Sponges.—Maas! has studied the fresh-water 
sponge in Berlin, He describes the segmentation of the egg and the 
process of formation of the germ-layers. The latter exhibits some 
similarity to gastrulation in its broader features, and results in the 
formation of a closed cavity at one end of the oral germ. From the 
seemingly similar cells of this germ the ecto- meso- and entoderm are 
developed. The ectoderm is at first distinctly columnar. The meso- 
derm cells soon acquire a distinctly mesenchymal shape, and begin 
the formation of spicules before the appearance of the ampulla. - The 
entoderm appears to develop from the lining cells of the cavity of the 
germ, and consists of a flattened epithelium connecting here and 
there with globular anlage of the ciliated chambers, These latter sink 
further into the mesoderm, the flattened epithelium becoming drawn 
out to form efferent canals. The efferent openings are produced by a 
thinning of the ectoderm and a final breaking through. Maas did not 
see the process of formation of the osculum. Soon after the differ- 
entiation of the germ-layers the embryo (which has previously led a 
‚free life) loses its cilia and settles down, at the same time becoming 
flattened into a thin sheet. Connected with this, the ectoderm loses 
its columnar character and becomes flattened. Maas gives more proof 
—if more was needed—that Gótte was wrong when he said that Spon- 
gilla loses its ectoderm during the process of development. 
Notes on Earthworms.—In a paper,? devoted chiefly to de- 
scriptions of genera and species, Mr. F. E. Beddard prints some inter- 
Indies and New Caledonia. Pericheta, from its distribution, 
from its nephridial system and its circles of chat (Lankester’s 
Testriction of the term sete is advisable), is regarded as the 
more primitive, and the bunches of chete in other earthworms are 
derived from this, rather than from the parapodia of some Polychzeta. 
In the posterior part of the body of Pericheta indica are peculiar 
glands attached to the posterior sides of the septa on either side of 
the dorsal vessel. Somewhat similar septal glands occur in Acantho- 
drilus. Chemical tests seem to show the presence of glycogen in these 
1 Zeit. Wiss. Zool., L. Heft a: 
* Proc. Zool. Socy. London, 1890, p. 52. 
