310 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
dorsal nerves. With regard to the motor system of nerves, it is pointed 
out that in Astacus the unit of the motor system consists of three parts : 
— (1) A single nerve-cell, which, from its histological characters and 
relations to the blood stream, appears to be a highly metabolic structure. 
This cell is removed by a considerable length of nerve from the direct 
track of the nerve’s impulses. (2) A single nerve process from this 
cell branches in a characteristic fashion, and consists of a number of 
elements suspended in a plasma. (3) The branches of this process, and 
therefore of the single nerve-cell. These are very numerous, are dis- 
tributed to the plexus of the ganglion, and to a very large mass of 
muscle fibres. The longitudinal commissures of the ventral cord appear 
to be connected directly with the plexus of the ganglion, and again with 
it by a "I" -shaped junction, and thirdly with cells whose processes merge 
in the plexus of the ganglion. In conclusion, the author points out that 
the nerve fibrils which pass to the fine plexus, enter it in well-defined 
bundles, which go to histologically distinct regions. This structural 
feature may be correlated with the fact that each nerve contains different 
grades of fibres, which supply either different muscles or regions of the 
sensory surface supplied by the nerve as a whole, which differ in the 
fact that stimulation of the one region or the other does not produce 
quite identical disturbances in the central nervous system. 
Flying Crustacea.* — Herr Al. Mrasek notes, under this somewhat 
sensational title, that Captain Hendorff has recorded two cases of 
Crustacea leaping out of the water. j* One was a Pontellid ( Pontella 
securifer Brady), which several times sprang almost a foot out of the 
vessel. The other referred to some Schizopod. The leaps are probably 
either playful or attempts to escape. 
Springing or Flying ? % — Dr. A. Ostroumoff thinks the “ flying ” of 
Pontellina mediterranean Cls. is indubitable, but he does not mean that 
the Crustacean can actively change its original direction of move- 
ment. In the same way the dolphin only springs or leaps, but Pteromys 
solans “ flies.” In English, the word “ fly ” is usually restricted by 
zoologists to cases in which there are active locomotor organs which 
beat the air, as in flying insects, flying birds, and bats. 
Embryonic Development of a Dicranodromia.§ — M. E. Caustier 
has had the opportunity of investigating some of the Promise collected 
during the deep sea dredgings of the Blake and the Talisman. Picra- 
nodromia ovata was found to carry large eggs 2 mm. in diameter. 
These eggs were found to possess all the cephalic and thoracic 
appendages, while the distinctly segmented abdomen was already pro- 
vided with plceopods. Although the embryo had thus already reached 
the Mysis stage, half of the yolk still remained to be digested at the 
stage which the author was able to study. The development of the 
appendages shows very well the extent of the affinities of this creature 
with the Anomura and the Macrura. These characters the author 
details. Particular attention is directed to the fifth pair of thoracic 
limbs ; these are folded on the back and directed forwards so that they 
* Zool. Anzeig., xviii. (1895) pp. 5-6. f See this Journal, 1894, p. 681. 
i Zool. Anzeig., xviii. (1895) p. 122. 
§ Comptes Eendus, cxx. (1895) pp. 573-5. 
