288 © The American Naturalist. [March, 
EMBRYOLOGY. 
The Star-fish Larva.—Dr. G. W. Field: has published a fully 
illustrated study of the development of our common star-fish obtained 
at the U. S. Fish Commission Laboratory, at Woods Holl, Mass. Spe- 
cial attention was directed to the mesenchyme, mesodermal pouches, 
ciliated bands and watervascular system of the larva with a view to, 
solving the meaning of the echinoderm larva. 
The two symmetrically placed outgrowths of the. archenteron 
acquire connection with the exterior by uniting with two dorsal 
ectodermal invaginations. These invaginations form two water 
pores, which are both open for awhile. The one on the right closes- 
up. This double condition isnot, as has been maintained, an abnormal 
condition, but as Professor W. K. Brooks showed, a normal and 
significant fact. 
In discussing the application of these and other facts to the phyllo- 
geny of the Echinoderms, the author holds that—‘the Echinoderm 
IFNA was ery a free-swimming animal, in general characters 
fthe Turbellarians ; a creature witha. 
well-differentiated digestive tract, ciliary locomotor apparatus, excretory 
system, respiratory surface not localized; coenogenetrically modified’ 
by the acquirement of transparency, long arms and particularly by 
modification of the external form, by changes in the direction of the 
ciliated bands, as pointed out by Johannes Miiller, into the forms. 
characteristic for the various Echinoderm groups.” 
Germ-layers of Amphioxus.’—Basilius Lwoff has recently 
published a short paper in which he gives the results of his observa- 
tions on the early stages of Amphioxus so far as they differ from those 
arrived at by Hatschek. 
He finds that there is no period of rest at the end of the cleavage, 
at least as far as the smaller ectoblastic cells are concerned, for they 
continue to divide frequently. This causes a change in the relative 
position of the cells at the boundary between the micromeres and 
macromeres, and results in the passive invagination of the entoblast,. 
ectoblastic cells being the active agents, 
1Q. J. Mic. Sci. 1892. 
*Biol. Centralblatt, 12, 1892, pp. 729-744, 8 figs. 
