ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
451 
in tlio sericteria (spinning-glands) of caterpillars. The tracheal 
capillaries do not, he finds, end in the sericterial cells, but pass into a 
fine plexus — the so-called tracheo-capillary plexus. This is a system of 
fine tubes which, like the tracheal capillaries, consist of a peritoneal 
layer and an intima, which is probably chitinized ; the tubes anastomose 
with one another, and the capillaries of various tracheal areas are 
connected with one another. The plexus lies beneath the membrana 
propria and between it and the sericterial cells, and broadens out over 
the whole cell ; it does not, however, lie in the plasma of the cell, but is 
separated from it by a thin membrane. 
Secretion of Silk by Silkworm.* — Prof. G. Gilson is of opinion that 
the silk of the silkworm is a regular secretion product. He bases this 
view on the facts that — the glandular tube is covered internally, through 
its whole length, by a transparent membrane ; this contains circular 
threads, and the spaces between them are filled with a network-formation. 
As the silk is always separated from the cells by a membrane, it cannot 
be the result of the direct transformation of the protoplasm. In the 
next place, the silk is not, as a rule, to be detected by any reagents in 
the body of the cell, but in some cases it becomes really visible. At 
the end of larval life, certain shining spherules were found in the cells, 
and the reactions of these were just the same as those of silk. If one 
impedes the excretion of the silk at the end of larval life, the cell-body 
becomes quite burdened with silk-spherules. It seems that the silk is 
made up within the protoplasm, and cast out through the meshes of the 
netlike membrane. A selection is probably made by the membrane 
itself among the several substances that are mixed with the liquid part 
of the protoplasm and the silk, and the substance that becomes the silk 
is cast out. The special apparatus of the silk-duct seems to regulate the 
diameter of the thread, which is often very irregular before it has passed 
through it, and probably also to regulate the thickness of the thread. 
Development of Hydrophilus piceus.f — Dr. Y. Graber has a critical 
notice of Dr. K. Heider’s memoir on the development of Hydrophilus 
piceus. Objection is raised to the statement that the primitive segments 
in Insects never enter into any relation with the rudiments of the 
extremities, and Stenobothrus is cited as a case. In other cases Dr. 
Heider is stated to have reported on what happens in Hydrophilus as if 
the facts were noted by him for the first time. 
Development of Chalicodoma muraria.J — Dr. J. Carriere has pub- 
lished a full account of the development of this bee. The egg is 
sausage-shaped, and the concave side is the dorsal. It is particularly 
well adapted for study, not only because of its transparency, but because 
the whole process of development is effected on the future ventral side. 
Several periods may be distinguished during development within the 
egg ; the first closes with the formation of the germinal membrane, the 
second contains the changes which occur from the commencement of the 
formation of the germinal layers till the complete closure of the embryo 
* Rep. Brit. Assoc., 1889 (1890) pp. 628-9. 
t Zool. Anzeig., xiii. (1890) pp. 287-9. 
X Arch. f. Mikr. Anat , xxxv. (1890) pp. 141-65 (1 pi.). See this Journal, ante, 
p. 322. 
