ZOOLOGY AND BOTANY, MICROSCOPY, ETO. 
511 
Digestive Apparatus of the higher Stenoglossa.* * * § — M. A. Amaudraut 
has a contribution to our knowledge of the anterior region of the diges- 
tive apparatus of these Mollusca. By most of their characters the 
Conidse and the Terebridse are allied to the Stenoglossa, but the anterior 
part of their digestive apparatus shows that they form an aberrant and 
terminal group in the series of the Prosobranchia. This is the result to 
which Bouvier was led by a study of their nervous system. 
New British Doris.f — Mr. W. Garstang describes, under the name 
of Doris maculata, a small dorid of striking appearance, which has 
been several times obtained at Plymouth, and which seems to be quite 
distinct from any form hitherto described. The feature which gives it 
its most distinctive appearance is the presence, on the back, of a number 
of conspicuously coloured tubercles connected with one another by a 
network of low ridges. These tubercles are all of different sizes, and 
there is a good deal of irregularity in their arrangement. 
Maturation and Fertilisation in Physa fontinalis.* — Herren K. v. 
Kostanecki and A. Wierzejski have studied in particular the behaviour 
of the so-called achromatin substances in the ovum of this Gastropod. 
The processes of maturation and fertilisation are carefully described, but 
we shall confine our report to the general conclusions. 
The authors start from Boveri’s results. Fertilisation is the union 
of two cells which are originally alike in protoplasm, nuclei, and centro- 
somes. In the course of differentiation the nuclei remain homologous, 
and the end of fertilisation is their union. But the other side of fertilisa- 
tion, namely, the stimulus to division, depends mainly on the protoplasm 
and centrosomes which have been differentiated in opposite directions. 
The spermatozoon is poor in protoplasm, the ripe ovum is weak as to 
centrosome ; they are physiologically complementary. But while Boveri 
lays main emphasis on the centrosome, which for our authors is only “ the 
insertion-centre of a system of rays,” they lay the main emphasis on the 
differentiation of the plasma. In the ovum the accumulation of deuto- 
plasm is so great that the mitotic forces are inhibited, the extrusion of 
the polar bodies is a final effort, and in the formation of the second the 
archoplasmic material is reduced to a minimum. This lack is supplied 
by the plasma grouped around the centrosome in the middle portion of 
the spermatozoon. The ray-system arising therefrom constitutes a new 
equilibrium in the ovum, re-coordinating around itself the plasmic rays 
or network, even including those which connect the nuclear framework. 
The sperm-centrosome thus gains in importance, while the ovum-centro- 
some dwindles and disappears. After the re-establishment of equilibrium, 
the matter is one of ordinary mitoses. 
Origin of Mesoderm in Paludina.§ — Dr. C. Tonniges finds from a 
study of Paludina vivipara that the formation of the middle layer begins 
soon after gastrulation, by a migration of ectoderm cells. The migration 
occurs from the ventral wall in a limited area, wdiicli represents the 
closure of the blastopore. It lasts during the period of narrowing and 
* Comptes Rendus, exxii. (1896) pp. 1424-7. 
t Journ. Mar. Biol. Assoc., iv. (1896) pp. 167-8. 
x Arch. f. Mikr. Anat, xlvii. (1896) pp. 309-S6 (3 pis.). 
§ Zeitschr. f. wiss. Zool., lxi. (1896) pp. 541-605 (2 pis.). 
