606 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
The flagellate cells of the larva in all cases become the collar-cells 
of the young sponge. Certain cells of the inner mass, distinguished 
by their vesicular nuclei and blastomeric characters, are capable of 
giving rise to collar-cells, as well as to the flat epithelium, &c., i.e. 
both to the dermal and to the gastral layer. 
Consequently, during the metamorphosis of type C, flagellate 
chambers are developed from “ cell-groups ” derived originally from 
cells with vesicular nuclei situated in the inner mass, as well as from 
the flagellate cells. 
In type D, however, hardly any cell-groups are formed, and conse- 
quently the gastral layer is developed almost completely from the 
flagellate cells of the surface layer. 
The cell-groups and the flagellate cells of the larva are to be con- 
sidered as belonging to the same class ; the hitter being developed on 
the outside, and consequently producing only flagella ; while the 
former originate inside, and ultimately develope both collars and 
flagella. 
All the cavities, canals, and surfaces are lined by cells possessing 
granular nuclei, which are capable of producing microscleres, even 
when they are situated in the flat epithelium of the surface layers. 
The megascleres are produced at first in cells with vesicular nuclei, 
which later on become granular. 
Some of the cells with vesicular nuclei plaster themselves to the 
surfaces of the flagellate chambers in the young sponge, and become 
pore-cells, their nuclei subsequently changing in character and becoming 
granular. 
There is always a residue of cells with vesicular nuclei which retain 
their blastomeric characters, and which are therefore capable of giving 
rise to the whole sponge. Some of these, or perhaps all of them, be- 
come wandering cells, and ultimately give rise to the gemmule which is 
capable of producing both the dermal and the gastral layers of the 
sponge. 
The collar-cells multiply by karyokinetic division, and, owing to the 
multiplication of the collar-cells in the flagellate chambers, the latter 
become separated into two groups, and so produce two daughter- 
chambers. 
The existence of choanocytes or collar-cells in the sponges, as well 
as their early appearance in the free- swimming larva, together with the 
ontogenetic method of differentiation found in the Ascones, the most 
primitive of sponges, incline the author to the conclusion that sponges 
have been evolved independently from Choanoflagellata. This conclu- 
sion is further strengthened by the consideration that collar-cells do not 
occur in any of the various phyla of the Metazoa. 
Maturation and Fertilisation in Sponges.* — Dr. Otto Maas points 
out that cytological questions are hard to answer in the case of sponges. 
Even as regards karyokinetic division, the reports of it have hitherto 
been so doubtful that its occurrence has been altogether denied by some. 
As to the phenomena of maturation and fertilisation scarcely anything is 
known. Maas has however found mitotic division with unmistakable 
* Anat. Anzeig., xvi. (1899) pp. 290-8 (12 figs.). 
