1044 The American Naturalist. [December, 
passive, or after a time is even cast off or degenerates; certain small 
ectoderm cells appear to migrate into the entoderm and are interpreted 
by Mr. Lang as there giving rise to a new entoderm. While a new 
basement membrane is soon formed over most of the budding area it 
remains indistinct or absent around the periphery; a solid outgrowth 
is thus formed, within which a cavity appears by the separation or 
rearrangement of the new entoderm and loss of the old; we thus 
arrive at the two-layered, hollow outgrowth commonly regarded as 
the earliest stage in the formation of the bud. 
Unfortunately the illustrations given by the author are not numer- 
ous enough to convey to the reader the same convictions that the study 
of series of sections might. The equally important and difficult ques- 
tions, the migration of ectoderm cells and their conversion into new 
entoderm seem to require a reinvestigation of the subject before we 
can be fully convinced that the ectoderm is really the only seat of pro- 
liferation in budding hydroids. 
Comparing this bud formation with embryonic processes, the author 
points out the close parallelism between the formation of new ento- 
derm by multipolar migration from the ectoderm of the bud and the 
formation of the entoderm of the embryo by migration of ectoderm 
cells of the blastula. 
Instead of regarding the process of budding in coelenterates as a 
modified fission of the adult we may refer it back to the blastula stage 
and explain it as acquired in some ancestral blastula form, as an ata- 
vistic representation of a non-sexual mode of reproduction in a blas- 
tula-like coelenterate ancestor. 
Similarly Seeliger has interpreted budding in Bryozoa as due to a 
process of twin-formation in the embryo. ` 
Budding in annelids, tape-wormis and scyphistomas, where all germ 
layers are concerned, may still be regarded as having arisen from 
regenerative processes. Budding in Salpa remains unexplained. 
Notes on Elasmobranch Development.'—Prof. Adam Sedg- 
wick brings forward some new facts and considerations tending to sup- 
port his theory of the origin of metamerism in animals and also 
making clearer his views upon many important questions illustrated 
by his observations upon the embryos of Scyllium and Raia. : 
The blastopore of elasmobranchs, immediately before it closes, is pr 
gated, narrow slit, slightly dilated in front, where it lies on the 
floor of the medullary canal, and more dilated behind (Balfour’s yolk- 
*Quart. Jour. Mic, Sci., June, 1892. : 
