ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
521 
compressed laterally are shells of females. Intermediate stages of the 
shape of the orifice probably belong to young males, or at any rate to 
forms in which the copulatory organ is not yet well developed. The 
author asks whether it is not possible to apply the results which he has 
obtained to fossil shells. D’Orbigny, as long ago as 1841, suggested 
that the differences in the shells of Ammonites might be due to differ- 
ences in the sexes of the animals that occupied them. Nothing definite, 
however, appears to have been yet attained. 
y. Gastropoda. 
Mesoderm Formation in Pulmonata.* * * § — Mr. T. Fujita has made a 
study of the early stages of Siphonaria lepida , and publishes a prelimi- 
nary notice of his results. The endo-mesodermic cell first establishes 
itself at the 19-cell stage. At the 27-cell stage it differentiates into an 
endoderm cell and the primitive mesoderm ; bilateral symmetry is fully 
established at the 33-cell stage. The primitive mesoderm cell segments 
into two lateral ones. At the 38-cell stage endoderm cells formed by 
division of three macromeres are added to the one already present. The 
mesoderm begins to be formed from the two lateral primitive mesoderm 
cells at about the 43-cell stage. 
Phytogeny of Gastropoda, j* — It will suffice to call attention to a 
summary by Dr. J. Thiele of papers by Dali, Haller, Pelseneer, and 
others, which have been published during the last eight years. The 
student of the subject will find it convenient to consult this essay. 
5. Lamellibranchiata. 
Early Stages in the Development of the Pholadidae.J — Mr. C. P. 
Sigerfoos has been employed by the U.S. Fish Commission in the study 
,of the natural history of the ship-worms, on account of their great 
economical importance ; a preliminary note on his investigations is now 
published. V\ ith regard to Pholas it is found that the first two planes 
of cleavage are meridional, and followed by an equatorial one. Segmen- 
tation is such that bilateral symmetry is not established till after the 
formation of the germ-layers. The endoblast cells divide into almost 
equal parts, and gastrulation is partly epibolic, and partly invaginate. 
The blastopore persists as the mouth. The first cilia are irregularly 
arranged ; the apical cilia are very large ; the embryo rotates on its 
long axis, in the direction of the hands of a watch. In addition to the 
mesoblast, as usually described, there is a second factor derived from 
the ectoblast after the embryo is free-swimming. A history of the egg 
of Teredo norvegica is almost exactly the same as that of Pholas , and the 
same is true of T. fimhriata. 
Parasitism of Larva of Anodonta on the Skin of Fishes.§ — Herr 
V. Faussek has studied the Glochidia on the fins of Osmerus eperlanus. 
During the first period of their parasitic life the larvee obtain all their 
* Zool. Mag., vii. (1895) pp. 89-93 (1 pi.). 
t Biol. Centralbl., xv. (1895) pp. 220-36. 
X Johns Hopkins Univ. Giro., xiv. (1895) pp. 78 and 9 (1 fig.). 
§ Biol. Centralbl., xv. (1895) pp. 115-25 (4 figs.). 
