DECEMBER 10, 1897.] 
bacteria. These are about equally divided 
between Europe and America, and there is no 
excuse for ignorance concerning them. 
F. A. Lucas, Secretary. 
ZOOLOGICAL CLUB, UNIVERSITY OF CHICAGO. 
OCTOBER, 1897. 
Two Cases of Mimicry.—The results of some ob- 
servations on the mimetic habits of the Syrphid 
flies of the genus Spilomyia were presented. S. 
fusca, Leow, which is dull black-banded and 
spotted with yellowish white, was frequentlyseen 
flying about in the shrubbery and feeding on the 
honey of some golden-rods that had sprung up 
in a clearing in the pine woods (Price Co., Wis.). 
This Syrphid resembles in size, form, color- 
ation and movements Vespa maculata and a 
smaller allied species of wasp, and was observed 
to occur in the same places and at the same 
time as these Hymenopterous models. A large 
female of S. fusca was masticated and found to 
have an agreeable flavor, the alimentary tract 
of the insect being full of honey in this in- 
stance. Therefore, warning colors are asso- 
ciated with the absence of disagreeable smell 
and taste, as the generally accepted theory of 
mimicry requires. In the same locality Spilo- 
myia quadrifasciata, Say, was less common than 
S. fusca. It strikingly resembles the species of 
Odynerus (O flavipes and O. foraminatus), which 
also frequent the flowers of the golden-rods. 
Both insects are black, spotted and banded with 
bright yellow, the black predominating. The 
genus Spilomyia includes also a third group of 
mimics, which, like §. lJiturata, Williston, 
closely resemble the ‘yellow-jacket’ wasps 
(V. germanica, etc.). In these flies the deep 
yellow bands are broader and more numerous 
and the black coloring more restricted than in 
S. fusca and S. quadrifasciata. 
W. M. WHEELER. 
Secondary Mesoblast in the Mollusca.—Sec- 
ondary mesoblast was first found in the mol- 
lusks in the lamellibranch Unio by Dr. F. R. 
Lillie. This secondary mesoblast was found to 
arise asymmetrically from a cell of the second 
generation of ectomeres on the left side of the 
ege. It subsequently becomes disposed sym- 
metrically on both sides of the egg, apparently 
by a migration of some of the cells, and is 
SCIENCE. 
887 
mainly employed in the formation of the larval 
adductor muscle. 
Later, secondary mesoblast was discovered in 
the gasteropod crepidula by Dr. Conklin. It 
was found to arise from the second generation 
of ectomeres, as in Unio, but from three quad- 
rants instead of one, and at a much later stage- 
of develepment than in the form studied by 
Lillie. 
The secondary 'mesoblast in Physa, accord- 
ing to Wierzejski, and in Planorbis, according 
to my own observations, has a still different 
origin, since it arises from cells of the third 
generation of ectomeres on the anterior side of 
the egg. Its origin is symmetrical, as it arises 
from the two anterior quadrants of the third 
quartette, which lie on either side of the median: 
plane. The divisions of the cells in the third 
quartette in Planorbis agree very closely with 
those of Physa until a [late period of cleavage. 
In both forms the first division of the cells of 
the third quartette is radial ; at the next divis- 
ion both the upper and lower cells in the two 
anterior quadrants divide horizontally into 
equal parts. The next cleavage in the anterior 
quadrants is the unequal division of the lower 
pair of cells, each cell giving off a small cell 
toward the vegetal pole. In both Physa and 
Planorbis the upper pair of cells resulting from 
this last cleavage contain the secondary meso-- 
blast. In Planorbis these cells, after dividing 
almost horizontally, sink into the segmentation 
cavity and finally lose connection with the wall 
of the blastula. Whether these cells are- 
entirely converted into secondary mesoblast in 
Physa, as in Planorbis, appears uncertain from 
Wierzejski’s account. S. J. Hommes. 
Dr. Whitman gave an account of his observa-- 
tions concerning the results of crossing the 
brown and the white varieties of ring-dove, and 
Dr. Watase read a paper entitled ‘ Protoplasmic 
Contractility and Phosphorescence.’ 
During the month the following reviews of 
recent} papers were also given: ‘The Embry- 
ology of Crepidula’ (Conklin), A. L. Treadwell ; 
‘Recent Literature on Spermatogenesis’ (Meves 
and Hermann), W. H. Packard ; ‘Structure of 
Nermertean Nerve-cells’ (Montgomery), G. W. 
Hunter. 
