248 SUMMARY OF CURRENT RESEARCHES RELATING TO 



from one another, those of Pyrosomes tend to intergrade. An interes- 

 ting general feature is that the individuality of the cell is not only 

 subordinated to that of the zooid, but in the case of some cells, e.g. 

 in the making of the test, to the colony as a whole without reference to» 

 the zooids. J. A. T. 



INVERTEBRATA. 

 MoUusca. 



Use of Toot in some Molluscs. — W. J. Crozier (Journ. Exper. 

 ZooL, 1!)19, 27, 359-60, 1 hg.). To types of locomotion in Molluscs 

 already described a new type is added, a " looping " movement seen^ in 

 Xenophora. It involves the body-musculature generally, but the suction 

 of the foot is also needed. It may be classed with the "gallop" of 

 Helix, though it has distinctive features. A second good example of 

 arhythmic pedal progression is described in species of Conus, and three 

 species of Chitons (in the genera Isclinochiton, Acanthochites, and Tonicia} 

 are added to the list of those Molluscs known to move by means of 

 retrograde pedal waves. It is noted that Isclinochiton can move pos- 

 teriorly, preserving the retrograde character of its pedal waves, with 

 considerable freedom and for appreciable distances. It also exhibits a 

 " gallop," such as Carlson has described in Helix, which is independent 

 of the pedal waves. J. A. T. 



a. Cephalopoda. 



Colour-sense in Octopus. — 0. Polimanti {Arch. Itol. Biol., 191.% 

 64, 293-300). There is extraordinary divergence of results in the 

 experiments that have been made on Cephalopods in regard to colour- 

 sense. Polimanti, working with Octopus vulgaris, has measured the 

 sensitiveness by the oscillations in the respiratory movements. He finds 

 that violet and blue light are most stimulating, green less, red still less. 

 But he inclines to the view that there is not in Octopus any perception 

 of colours. He thinks that differently coloured lights affect the meta- 

 bolism, and that the changes in metabolism affect the respiratory move- 

 ments. But it is evident that more experiments are required. 



J. A. T. 



y. Gastropoda. 



Sensitiveness of Gill-plumes of Chromodoris zebra. — W. J. 

 Crozier {Proc. Amer. Physiol. Soc, 2>lst Meeting, in Amer. Journ. 

 Phijsiol., 1919, 49, 147). Between 15° and 32°, and in sunlight not 

 too intense, the gill-plumes of this Nudibranch respond by contraction 

 when they are shaded. This contraction, due to the activation of recep- 

 tors locally contained, leads to the reflex retraction of the gill crown as 

 a whole within its collared pocket. The degree of extension of the gill 

 crown as a whole is a function of the light intensity, but is controlled 

 through a separate set of receptors. The animal is photokinetic. The 

 sensitivity of the plumes to shading is abolished if the alkalinity of the 

 water is reduced. The " protective " reaction to shading is a response 



