SCIENTIFIC SUMMARY. 
443 
tion is suggested ; or the jet itself may be observed if illuminated by the 
same spark diffused by passing through ground glass. The electrically 
maintained fork may be made to perform the double office of controlling 
the resolution of the jet, and of interrupting the primary current of the 
coil. The jet then illuminated in only one phase appears perfectly steady, 
and may be examined at leisure. In an appendix to this powerful but 
graceful monograph, the mathematical investigation of the motion of friction- 
less fluid under the action of capillary force, in the form of an infinite 
circular cylinder, and the vibrations of a liquid mass about a spherical 
figure, is worked out at some length. 
ZOOLOGY. 
Morphology of the Nervous System in Dipterous Insects . — Mr. J. Kiinckel 
has lately communicated to the Academy of Sciences ( Comptes rendus, 1 Sep- 
tember, 1879) a summary of the results of his researches upon the nervous 
system in the Diptera. He finds that in the arrangement of the ganglia 
forming the central chain, there may be a close centralization or union of the 
whole into an almost continuous mass, or an extreme separation of the 
nervous centres, with the most various intermediate groupings ; but, at the 
same time, each family has its nervous system constructed upon a peculiar 
and invariable plan. One of his most curious results, is the discovery that 
in certain groups, namely, the Stratiomyidae, Tabanidse, Syrphidae, Cono- 
pidae, and certain Muscidse Acalypterae, the ganglia which were originally 
united in the larva become separated during the passage of the insect into 
the pupa ; so that instead of being shortened, as in many insects, by the 
approximation of the ganglia, and the fusion of some of them, in these flies 
the ganglionic chain is actually lengthened in the imago, and some of the 
ganglia are passed into the abdomen. 
In accordance with the evolution of the nervous system, M. Kiinckel 
suggests that the Diptera may be divided into three groups: — 1. Those 
which follow the ordinary law, and in which some of the ganglia become 
fused together during the passage to the pupa stage (the Nemocera of the 
older Entomologists) : — 2. Those in which the ganglia separate at the same 
epoch (the families above-mentioned) : — and 3. Those in which the thoracic 
and abdominal ganglia remain confounded, as in the larvae (Muscidae Calyp- 
terae, (Estridae, Hippoboscidae, Nycteribiidae). In all Diptera the ganglia 
are distinct and clearly separated in the embryo. In the larvae of the first 
group they remain distinct ; in those of the two other divisions, they tend 
constantly to approach each other, their coalescence increasing with the 
growth of the larvae. In the pupae of the second group there is a phenome- 
non of reversion, the nervous centres again separating ; whilst in the pupae 
of the third group they remain associated in a single mass. 
M. Kiinckel passes in review the families of Diptera, which, as he says, 
differ in the value of the external characters on which they are based, and 
indicates the following as approximately equivalent groups : — the Hippobos- 
cidae, Nycteribiidae, (Estridae, and Muscidae Calypterae, which have the 
thoracic and abdominal centres united into a single mass, may form a special 
