ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
751 
Porifera. 
Classification of Sponges.* — Dr. R. v. Lendenfeld gives a compila- 
tion of our knowledge of tlie characters of Sponges, in which the genera 
are defined and a phylogenetic scheme offered. An alphabetical list is 
appended of the names given to the various forms of sponge-spicules, 
and there is also a bibliography of authors quoted. 
Development of Spongilla fluviatilis.j — M. Y. Delage finds that, 
in the development of the fresh-water Sponge the ectoderm is formed at 
the expense of cells which were primitively internal ; the ciliated cells 
take no part in its formation, for they pass into the interior of the body, 
where they are seized on by the amoeboid mesodermic cells, and later on 
take part in forming the chambers and canals. This capture of the 
ciliated cells is, fundamentally, only a phenomenon of phagocytosis, which 
is incomplete in that it is temporary ; some of the cells do, indeed, 
appear to be truly digested ; it is probable that at the moment when 
they lose their cilia they undergo a temporary diminution of vitality, 
and that the amoeboid cells capture them, but are unable to digest them. 
The author remarks on the interest of a fact of this kind becoming a 
normal phenomenon of development; it recalls to him the histolytic 
processes seen in Insects, but with this great difference, that here the 
elements incorporated by the phagocytes are utilized in future histo- 
genesis directly, and not as simple nutrient materials. 
Protozoa. 
Successive Regeneration of Peristome in Stentor.J — Prof. E. G. 
Balbiani finds that in Stentor cseruleus , and probably also in other 
species of the genus, the region of the peristome near the mouth, the 
mouth, and the oesophagus occasionally become atrophied ; but the 
atrophy is soon followed by the complete regeneration of these parts. 
The regeneration commences with the formation of a new peristome and 
of a mouth which appears at the sides, before occupying the normal 
position at the anterior pole of the body. A new peristome may be 
easily recognized by the changes in its system of striation ; it is divided 
into secondary areas, each of which has its own striation, and of which 
the number increases with the age of the animal. When these areas 
are multiplied they give the peristome a mosaic appearance which is 
more or less regular, and the degree of complication allows of an 
estimate of the age of the individual. 
When the newly formed peristome changes its lateral for its terminal 
position, movements of contraction are seen in the nucleus ; the result 
of this is the concentration of all its joints in a common rounded mass ; 
when the change of position is effected the nucleus regains its monili- 
form appearance. All the phases of the nucleus are like those which it 
undergoes during division, except that it returns to its primitive number 
of joints. These changes in the form of the nucleus correspond, either 
on fission or reparation, with the stages in the displacement of the new 
* Abhandl. Senckenberg. Naturf. Ges., xvi. (1890) pp. 361-439 (1 pi.), 
t Comptes Rendus, cxiii. (1891) pp. 267-9. 
t Zool. Anzeig., xiv. (1891) pp. 312-6, 323-7 (6 figs.). 
