730 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
the polar globules are typically developed at the pole nearer the mother, 
as stated by Kleinenberg, and not on various points of the surface, as 
asserted by Korotneff. The granules in the globules are not yolk- 
spheres, but of nuclear origin. The equal segmentation leads to a 
blastula, which is composed of cells of equal and not unequal size. The 
cleavage-cavity is seen in the eight-celled stage. The endoderm is not 
formed by polar immigration of cells, but is multipolar; blastoderm- 
cells partly loose themselves from their connections and wander into the 
cleavage-cavity, partly undergo division, and the inner portions form 
endodermal cells. The ectoderm is not lost when the egg-shell is 
formed, but persists ; the shell is a cuticular structure. 
Porifera. 
The Genus Stelletta.* — Dr. E. von Lendenfeld gives a monographic 
account of the genus Stelletta , describing five species, viz. S. grubei, 
S. dorsigera, S. boglicii , S. pumex , and S. hispida. They are “ siliceous 
sponges, with triaen and amphiox megascleres, and with rigidly radial 
asters, with which rhabdodragmata are rarely associated ; with small 
spherical ciliated chambers, and mostly with a rind.” It may be noticed 
that the technical names of sponge-spicules have been recently! ar- 
ranged, and the forms illustrated, by Prof. F. E. Schulze and Dr. 
Lendenfeld. 
The peculiar “ chones ” which Bowerbank first noticed, and which 
Sollas first described with due carefulness, are discussed at some length. 
“In most Tetiactinellids with thick rinds, and also in Monactinellids 
such as Sollasella, the pore-canals unite in groups into larger main-canals, 
which penetrate the rind. In the lower portion of the main-canal in these 
sponges there is a marked constriction which divides it into a distal 
portion (the inhalant main-canal) and a proximal portion (the chonal- 
cupola of the subdermal space). Sometimes, as in Stelletta boglicii and 
S. hispida , the constriction lies at the inferior end of the canal, where it 
opens into the subdermal space. In these forms the chonal-cupola is 
absent. The tissue which forms the constriction consists of flat, elon- 
gated, or in part spherical cells, forming a thick mass in the neighbour- 
hood of the narrow chonal canal which passes through the constriction. 
These cells are more or less concentrically arranged, but in the Adriatic 
species of Stelletta there are not simple circular muscle-fibres, as Schmidt 
and Sollas maintained. As Auchenthaler correctly noted, they are cells 
which by their turgescence are able to narrow and close the chonal 
canal, and thus to regulate the stream of water.” 
Development of the Freshwater Sponge.}: — Dr. 0. Maas finds that 
the egg of Spongilla is rich in yolk, that it undergoes total and equal 
segmentation, and gives rise to a compact morula. The cavity formed 
at one pole of this morula closes up before the cells have lost the 
character of blastomeres. The differentiation of the tissues begins 
simultaneously at all points of the embryo, and so gives rise to a tri- 
laminate larva. The mobile larva consists of an outer layer, formed of 
cylindrical, ciliated cells ; of an epithelial lining, formed of flat spindle- 
* Abhandl. K. Preuss. Akad. d. Wiss., 1889 (1890) p. 75 (10 pis.). 
f Op. c., i. p. 35. % Zeitschr. f. Wiss. Zool., 1. (1890) pp. 527-54 (2 pis.). 
