CXVil 
donbt but that they have thus the power of conveying other sentiments 
and ideas to one another. 
In conjunction with M. Thelen, Dr. H. Landois has also communi- 
cated to the Zeits. f. Wiss. Zool. another memoir, on the means by 
_which the spiracles, or rather the trachee immediately behind the 
_ spiracles, are opened or closed. The mechanism consists of four 
principal parts, the bow (verschlussbugel), the lever (verschlusskegel), 
the band (verschlussband), and the muscle (verschlussmuskel). The 
contraction of the latter, acting on the lever, causes the band and bow 
_ to meet, and thus close the passage. When the muscle relaxes, the 
natural elasticity of the parts causes them to separate again, and thus 
leave the tracheal tube open. They describe the details of the appa- 
_ ratus in a considerable number of species. * 
Dr. H. Landois has also published a memoir on the ocelli of cater- 
_ pillars. After describing them in detail, he comes to the conclusion that 
they do not essentially differ from compound eyes, and that if many of 
them were grouped together they could hardly be distinguished from 
compound eyes. In each so-called ocellus the cornea is divided into 
three*lenses, corresponding to three nerves, each with a separate ter- 
minal enlargement forming the so-called crystalline bodies. Each 
ocellus therefore might be regarded as in reality composed of three. 
On the other band, the three arches of the cornea are so closely 
connected together that they give the impression of forming a 
single cornea. The three lenses also are very closely pressed, and 
the three nerves unite into one. Under these circumstances Dr. 
Landois regards the ocelli of caterpillars as a connecting-link between 
single and compound eyes, and proposes for them the name of $ ocelli 
compositi.’+ 
Dr. August Weissmannjf has published a long and interesting memoir 
on the metamorphoses of Corethra plumicornis. The larva of this fly 
is the beautiful transparent creature, about half an inch in length, 
which all Jovers of Natural History must have watched floating hori- 
zontally among the green vegetation of our clear ponds, and ready, in 
spite of its apparent delicacy and crystalline transparency, to pounce 
on any little unwary victim which may come within its reach. At 
* Zeits. f. Wiss. Zool. 1867, Vol. xvii. Pt. 2. 
+ Zeits. f. Wiss. Zool. Vol. xvi. Part 1. { Id. 
