ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
G09 
The male gonopliores of Distichopora occur in groups of two or three 
in each ampulla, in different stages of development. The gonad is 
supported by a small cup-shaped trophodisc and inclosed in a double sac 
of ectoderm and endoderm. At the distal pole of the ripe gonopliore 
there is a short seminal duct. The male gonophore of Allopora differs 
from that of Distichopora in being provided with a club-shaped endo- 
derm al manubrium. 
The author does not regard the gonopliores of the Hydrocorallinae as 
degenerate Medusae, but as special organs of the colony bearing the 
gonads. This may jmzzle those who believe they should draw a sharp 
distinction between the idea of the “ individual ” and the “ organ ” in 
the Animal Kingdom, but Dr. Hickson is not inclined to believe that it 
is possible to draw this sharp distinction ; they are, as Claus maintains, 
relative ideas. 
Although the classification of the Hydrocorallinae with the Hydroidea 
was perfectly justifiable at the time it was made, the progress of our 
knowledge seems to point to the separation of the former from the latter, 
that is from the Tubulariie and Campanularise. 
Craspedota of the Plankton Expedition.* — Dr. 0. Maas concludes 
as to the Craspedote Medusae of the Plankton, (1) that the Aglauridae 
occur chiefly in the northern part of the Atlantic Ocean, (2) that these 
are replaced in the median region by the Trachynemidae, (3) that the 
Geryoniidae have a more southern distribution and increase in the number 
both of species and individuals towards the equator. But there are 
many individual exceptions. 
Development of Hydra.t — Dr. A. Brauer finds that the ova of Hydra 
are developed in the interstitial cell-layer ; one cell of the ovary becomes 
the egg-cell, while the others are broken up and their substance con- 
verted into yolk-grains, the so-called pseudo-cells ; these are taken up 
by the growing cell. Cleavage is total and equal and leads to the 
formation of a large hollow blastula. The formation of the endoderm, 
which is multipolar, is effected by immigration and division of the blasto- 
derm-cells. After the disappearance of the cleavage cavity the two 
germinal layers are sharply separated from one another. The ectoderm 
gives rise to an outer envelope, the chitinous shell, and an inner one 
which is the internal germinal envelope. The ectoderm is retained and 
passes into the permanent ectoderm. While the germ is still surrounded 
by the shell the layer of interstitial cells is formed from the ectoderm. 
The differentiation of tissues begins after this, the supporting lamella 
becomes recognizable, and the body-cavity begins to be formed. At the 
same time the shell disappears. When the embryo has become free the 
processes of development go on rapidly, the tentacles are formed and 
the mouth appears. The oral pole is identical with the pole of the 
directive corpuscle. 
It would appear that the method of multipolar endoderm-formation 
is limited to the Coelenterata, and, among them, is seen only in those 
forms in which there is no free-swimming blastula stage ; all the forms 
that have a free-swimming blastula exhibit a polar formation of the 
* SB. K. Preuss. Akad. d. Wiss., 1891, pp. 333-8. 
t Zcitschr. f. Wiss. Zool., lii. (1891) pp. 169-216 (2 pis.). 
