ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
185 
tide ; these are Geophilus ( Scotioplanes ) maritimus and G. ( Schendyla ) 
submarinus. There is nothing extraordinary in this resistance, for 
essentially terrestrial Geophili can exist in sea- water from twelve to 
seventy hours, and in fresh water from six to ten days. Forty-six 
genera and nearly eighty species of Arthropods are known to frequent 
the shores and to allow themselves to be submerged, though they breathe 
air. This resistance is not due to any special structure but to the general 
property of abranchiate Arthropods of being able to resist asphyxia for 
a long time. Swimming insects, such as the Dysticina which take with 
them a layer of air, resist submersion for a shorter time than insects 
which are exclusively terrestrial ; this appears to be due to the greater 
activity of swimming insects in water and to the consequent using up of 
the oxygen possessed by them. 
5. Arachnida. 
New Genus of Leaping Acari.* — M. Topsent and Dr. Trouessart 
describe a new form of leaping Acari which they call Nanorchestes 
amphibius ; it was found on the shore at Calvados. The animal leaps so 
actively that the only way to catch it is to have pincers dipped in oil or 
glycerin. At first sight, nothing in the structure of the animal indicates 
the extreme agility of which it is possessed. The very sharp distinction 
between the abdomen and the cephalothorax, the presence of a single 
hook at the extremities of the legs, and other characters distinguish this 
form from any of the Eupodinse, in which sub-family it may be placed. 
The form of the legs does not offer any explanation of the mechanism of 
leaping, for the hinder legs are no different from the others. It is 
probable that the animal folds its four pairs of legs under it and springs 
by suddenly separating them ; the form of the tarsus would support this 
explanation. 
Pycnogonidea of N orwegian North Sea Expedition. - ) - — Prof. G. 0. 
Sars gives detailed descriptions and drawings of all the species collected 
by the Norwegian North Sea Expedition, the material for which was 
very copious. This, with other specimens at his disposal, has enabled 
the author to acquire a good general view of the Pycnogonidian fauna 
of the Northern and Arctic Seas. The large number of species of 
Nymphonidse is found to be eminently characteristic of the Northern 
Seas as contrasted with the Mediterranean, and the northern forms are 
also as a rule much larger ; some are even gigantic. 
Owing to the present unsatisfactory condition of the terminology 
employed for the various parts of a Pycnogonid, the author has a 
number of changes to propose, which are explained by a diagrammatic 
figure. Great care has obviously been taken with the determination of 
the species, and those now given as new, of which there are eleven, have 
already been noticed in brief preliminary descriptions. 
The general systematic classification of the group is in an unsatis- 
factory condition, for now that it is recognized that the Pycnogonidea are 
neither Crustacea nor Arachnids, it is necessary to try and group the 
* Comptes Kendus, cxi. (1890) pp. 891-2. 
f ‘ Den Norske Nordhavs-Expedition 1876-78. XX. Pycnogoniden,’ by G. O. 
Sars. Christiania, 1891, 163 pp., 15 pis. and 1 map. 
