ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
183 
on the anatomical discovery of probable sound-producing and sound-per- 
ceiving structures, Wasmann is naturally very cautious as to the 
conclusiveness of his own observation. 
Development of Chironomus.* — Herr R. Ritter has reinvestigated 
the development of the reproductive organs, and has shown by means of 
sections that they arise from previously extruded “ pole-cells ” as 
Metschnikoff suggested, and as Balbiani carefully described. But as 
Balbiani did not make sections of the embryos, Ritter’s corroboration 
is of much value, for he has followed the “ pole-cells ” from their 
appearance at the posterior pole of the ovum before the blastoderm is 
formed, through their stages of division and subsequent insinking, to 
their establishment as reproductive organs. By his sections Ritter has 
also confirmed what Weismann described in regard to the invagination of 
the hind-gut, while he agrees with Graber in referring the wall of the 
mid-gut to two lateral strands which arise from the union of segmen- 
tally disposed endoderm. His results are antagonistic to Voltzkow’s, 
according to which the wall of the mid-gut arose by proliferation from 
fore and hind-gut. 
After patient watching, Ritter was able to observe the nocturnal 
egg-laying. The insects after much hesitation lighted on the sides of 
the aquarium a little above the level of the water. A chain of eggs 
connected by gelatinous material is extruded on to the water ; the jelly 
swells, and the chain floats. When the process is finished (in about five 
minutes), the insect moors the floating eggs by glueing the proximal 
end of the chain, and flies away. The author gives some interesting illus- 
trations of the insect’s marked preference for localities where the eggs 
are least likely to be frozen. 
Histology of the Gut in the Larva of Ptychoptera contaminatat— 
Prof. A. van Gehuchten has studied the histology of the gut in this 
Dipterous larva. In the oesophageal valve there is a remarkable 
vascular cavity between the proventricular epithelium and the muscular 
tunic. It is traversed by a muscular and elastic network with blood in 
the meshes. The lamellae and fibrils of the network consist solely of 
plasmic reticulum without any enchylema. In this fact the author finds 
support for his theory of the structure of muscle, which he discusses at 
some length. The protective marginal portion (or “ plateau ”) of the 
secreting cells is described very carefully ; it is produced by a 
differentiation of the plasmic framework, and exhibits much complexity 
and variety. Like the nucleus it is passive during secretion. 
Mechanism of Secretion in Larva of Ptychoptera contaminata. J — 
Prof. A. van Gehuchten finds that the glandular epithelial cells of the 
mesenteron of the larva of this dipterous insect are well adapted for the 
study of the mechanism of secretion. The cells are provided with a 
protective cuticle which prevents external lesions. The products to be 
eliminated are formed in the body of the cell in consequence of the 
special activity of the cell ; the elaborated products raise the covering 
* Zeitschr. f. Wiss. Zool., 1. (1890) pp. 408-27 (1 pi.). 
t La Cellule, vi. (1890) pp. 185-289 (6 pis.). 
X Anat. Anzeiger, vi. (1891) pp. 12-25 (7 figs.). 
