644 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
A. Gastrula formed by invagination of large segmentation cavity : 
e. g. Cotylorhiza, Pelagia noctiluca , and Nausithoe. 
a. Intermediate form between types A and B are found in Aurelia 
flavidula , in which the clump of cells that are invaginated is at 
first solid, and in Cyaneea capillata , in which this clump re- 
mains solid longer than in A. flavidula. 
B. A solid planula (sterrula) formed by hypotropous immigration of 
cells into a large segmentation cavity : e. g. Clytia , Tiara , 
Obelia , Cyansea arctica , &c. 
Intermediate forms in which the migration takes place mainly at 
the hind end occur in Mitrocoma. 
C. Sterrula formed by polypolar immigration of cells into a large 
segmentation cavity : AEginopsis. 
D. Planula formed by primary delamination ; a large segmentation 
cavity : e. g. Geryonia. 
d. There are numerous intermediate forms in which the segmenta- 
tion cavity is small. 
E. Sterrula formed by precocious delamination ; no segmentation- 
cavity : e. g. Aglaura , Eudendrium, &c. 
e. Intermediate forms have the segmentation at first incomplete : 
e. g. Benilla and Gorgonia. 
F. A multinucleated plasmodium ; no segmentation, and no segmen- 
tation cavity : Millepora, Stylasteridae. 
Dr. Hickson suggests that there is now much evidence to support the 
view that considerable phylogenetic significance is to be ascribed to the 
plasmodium stage ; he urges that too much weight has been given to the 
presence or absence of yolk, and that we should not expect that, when an 
ovum segments, it is simply repeating an ancestral phase, and that when 
it does not segment it is prevented from doing so by the physical ob- 
struction of yolk. 
In conclusion the author discusses the fragmentation of the oosperm 
nucleus ; the general results at which he arrives are : — (1) Fragmenta- 
tion of the nucleus is a normal method of nuclear division, and is not 
always a sign of pathological change. (2) In many cases in which the 
nucleus is supposed to disappear there is, as a matter of fact, minute 
fragmentation. (3) Fragmentation only occurs where there is no cell 
division. (4) Karyokinetic division of the nuclei is caused by the 
forces in the cell protoplasm, which bring about the division of the cyto- 
plasm. There is a series of phenomena in the division of the nuclei, 
with typical karvokinesis at one end, and direct fragmentation at the 
other. In Dr. Hickson’s opinion, the occurrence of any one kind or the 
other is determined by the forces which act simultaneously upon nucleus 
and cell-plasm ; and this view seems to be supported by the observations 
of Flemming and of Burger. 
Protozoa. 
Intranuclear Bodies.* — Dr. L. Rhumbler discusses the little bodies 
which occur in very variable number, size, and form within the nuclei 
of many Protozoa, and also within the germinal vesicles of Metazoa. 
* Zeitschr. f. wiss. Zool., lvi. (1893) pp. 328-64 (1 pi.). See this Journal, ante, 
p. 494. 
