ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 533 
cations issuing from adjacent cells. There is no doubt that there are 
distinct anastomoses between individual neurons. 
Between the bipolar Rath-Retzius elements, which represent isolated 
neurons, and the network of multipolar cells without axis-processes, 
there is a transition, namely, in those cells which not only share in the 
formation of the subepithelial plexus and the nerve network, but also 
have very long axis-processes. 
The phylogenetic series is probably as follows : — (1) The primitive 
lowest stage is that of a continuous quite peripheral network of nerve- 
cells, as in Ctenophora. (2) A second stage is found in cases where, 
besides the continuity of the sub-epithelial plexus, there are some cells 
with axis-processes which come into contact with other neurons in the 
central system. (3) In a third higher stage, the cells with axis-pro^ 
cesses lose continuity with the cells of the plexus, sink inwards from the 
periphery, and approach the nerve-centres. Thus arise the isolated 
bipolar neurons of the Rath-Retzius type in the crayfish. 
Respiration of the Crab.* — M. Georges Bohn has studied the 
respiration of Carcinus msenos, which lives almost as much in air as in 
water. He has observed a reversal of the direction of the water current 
in the branchial chamber, as may be readily seen if the crab is placed 
in a vessel with just enough of water to cover it. It raises the front of 
the body to the surface, and bubbles of air are seen to pass out by the 
usual inspiratory orifices. The crab aerates the water in its branchial 
chamber by a modified action of the scaphognathite, which drives the air 
backwards. Bohn compares his observations with those of Garstang on 
Corystes , and notes that reversal occurs also in Hyas , Maia , Palsemon , 
Megalopa larvae, crayfish, and others. In fact periodic reversal is an 
old-established habit, which here and there has come to be of much 
physiological importance. 
Hew Terrestrial Isopod.j — Prof. Baldwin Spencer and Mr. T. S. Hall 
describe Phreatoicopsis terricola g. et sp. n., a burrowing Victorian Iso- 
pod, closely related to Phreatoicus described by Chilton. The generic 
diagnosis is as follows : — Body long, subcylindrical, laterally compressed. 
Upper antennae short, lower long, with flagellum. Mandible with an 
appendage. First pair of legs subchelate, others simple. The legs are 
divided into an anterior series of four and a posterior series of three. 
Pleon long, of six distinct segments, but joined to telson. Uropoda 
biramous, short and powerful. Telson large, sharply truncate. 
North American Species of Cyclops.f — Mr. E. B. Forbes gives a 
descriptive account often North American species of Cyclops s. str. Claus. 
Of the eighteen species and three varieties which have been reported as 
occurring in North America, only three species, C. ater , C. modestus , and 
C. edax , and two varieties, insectus and brevispinosus , of C. viridis , are 
characteristic of America, while the remaining fifteen species and one 
variety are common to both Europe and America. 
Copepods of MoscowJ — M. Paul Matile describes the free Copepods 
found in the environs of Moscow. There are four genera, Cyclops , 
* Comptes Rendus, cxxv. (1897) pp. 441-4. 
t Proc. R. Soc. Victoria, ix. (1897) pp. 12-21 (2 pis.), 
j Bull. Illinois Lab. Nat. Hist., v. (1897) pp. 27-82 (13 pis.). 
§. Bull. Soc. Imp. Nat. Moscou, 1897, pp. 113-39 (1 pi.). 
