ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
117 
enclosed in two capsules ’of a milk-wliite colour and cartilaginous con 
sistency. The egg, with its outer covering, may be as much as 45 mm. 
long ; the yolk is of a rich-brown colour and very fluid ; the large quan- 
tity present points to the occurrence of a long period of incubation. 
The breeding of this creature, as of so many other forms, appears to be 
subject to a definite law of periodicity. 
y. Gastropoda. 
Yolk-Lobe and Centrosome of Fulgur.* * * § — Prof. J. Playfair M‘Mur- 
rich described some years ago (1886) the occurrence of a single large 
yolk-nucleus in Fulgur carica, but he now finds that this was a mistake. 
What he took to be a large polar globule is simply a small yolk-lobe 
comparable to that which occurs in many Gastropods. There are two or 
three true polar bodies. He describes the centrosomes and “ astrocoels ” 
observed at the stage preparatory to the appearance of four cells, and 
notes that the rapid increase in size of centrosomes and astrocoels begins 
just when the formation of the equatorial plate is completed, i.e. just 
when the movement of the chromatin towards the equator of the spindle 
ceases. 
The Genus Doriopsilla.'j' — Hr. B. Bergh established this genus in 
1880, on the strength of two specimens from Lesina, in Dalmatia, but 
he has not until recently been able to procure any others. Two more 
have been found by Dr. A. Nobre (Foz do Douro-Porto), and their dis- 
tinctiveness from Doriojpsis is confirmed. They are stiff and almost 
brittle animals, and the back has a granular appearance, thus differing 
from the soft and smooth-backed Doriojpsis. The buccal ganglia, instead 
of being behind the central system, are shunted forwards towards the 
end of the suctorial apparatus. A general description is given. 
5. Lamellibranchiata. 
Dreissensia polymorpha.f— Prof. J. Frenzel maintains, on the basis 
of many observations, that the colonies of Dreissensia can move en bloc , 
without separation of the individuals being necessary. When winter 
approaches the colonies move gradually from the shallower regions, and 
no isolated individuals are to be found. 
As to the actual movement, Frenzel notes that the young forms have 
three modes of motion (1) they fix their foot and draw the body after 
it ; (2) they push their way with their foot behind ; and (3) they clap 
their valves. The movement of the colony is probably altogether due to 
the younger members, for the foot eventually degenerates. Perhaps the 
strangest fact is the apparent unanimity within the colony, whose bond 
is little more than that of chance association. The author acutely 
suggests that the dissenting members break themselves off. 
Anatomy of Sphsermm soleatum.§ — Mr. G. A. Drew has recently 
sent us a short account of the anatomy of this Cyrenid, which is intended 
as an introduction to an account of the comparative anatomy of the 
* Anat. Anzeig., xii. (1896) pp. 534-9 (4 figs.). 
f Zool. Jahrb. (Abth. Syst.), ix. (1896) pp. 454-8. 
X Biol. Centralbl., xvii. (1897) pp. 147-52. 
§ Proc. Iowa Acad. Sci., iii. (1895) pp. 173-82 (3 pis.). 
