PHYSIOLOGY AND BIOLOGY. 
Ech. 43 
The two nervous systems, though quite distinct in function and activity, 
can work co-ordinately. The diffuse nervous system has the special 
function of perception and sensation, and the condensed nervous system 
is the centre of motor reaction. 
The authors further describe the influence of poisons and of heat on 
Asterias rubens. 
Durham finds that insoluble particles introduced into the body-cavity 
of Asterias rubens are ingested by leucocytes, which then make their 
way through the walls of tho dermal branchice to the exterior and dis- 
integrate. Similarly leucocytes containing refringent spherules, which are 
products of normal metabolism, emigrate from the body, and by their 
disintegration produce a brownish slime on the exterior. This process 
occurs both in the dermal branchiae of Asterias, and in the ambulacral 
branchiae of Echinus sphcera. Jn the latter case the spheruliferous cells 
of the branchiae differ from those found in the dorsal organ. In Sj)a- 
tangus purpureas and Amphidotus cordatus , the process of removal of 
products is associated with the formation of pigment, and takes place (1) 
at any part of the surface of the body ; (2) in the neighbourhood of the 
rosette feet, and in the feet themselves ; (3) into the tubes of the madre- 
porite, from whence the leucocytes probably wander to the exterior, if 
not carried out by an efferent current. 
The author compares these results with those obtained in other groups 
of the animal kingdom, and discusses the phenomenon of excretion from 
the skin. It is pointed out that if (excretory) pigment granules are 
brought to the surface more rapidly than they are got rid of, pigmenta- 
tion will ensue, and that pigment which has dono its work may bo thus 
retained to colour the individual. 
The hpemal system, with its central dorsal organ (ovoid gland), is 
regarded as an apparatus for distributing nutrient substances along the 
body, for producing amoeboid corpuscles, and for the working up of effete 
material. The only methods of communication between the haemal system 
and other spaces is (1) by osmosis ; (2) by diapedesis of corpuscules. 
For the influence of freshwater on Echinoderms ( Antedon rosacea , 
Synapta inhairens , various Ophiurids and Starfish) see Gogorza. 
Jaekel (2) discusses the mode of life of the Ilolopocrinidce. They are 
inhabitants of coral reefs in shallow water, and subject to strong cur- 
rents, with reference to which the animal has an oblique position on the 
stem, so that the ventral surface is turned towards the current. The 
arras inserted higher up are generally more strongly developed than those 
lower down. 
Loeb describes experiments to show that Cucumaria cucumis is obliged 
to maintain a certain position in relation to gravity, always remaining 
attached to vertical surfaces or creeping on them. It is shown that light, 
want of oxygen, &c., have no influence in bringing about this result, 
which depends on the effect of gravity only. Asterina gibbosa is nega- 
tively geotropic. Asterina tenuispina , on the other hand, is not geo- 
tropic, but is positively heliotropic. 
