32 



HARDWICKKS SCIENCE-GOSSIP. 



of an orange colour. Here the yellow paper reflects 

 red, yellow, and green rays into the eyes ; but the 

 sensation of green is worn out and we perceive only 

 the red and yellow rays, and these we know give 

 rise together to the sensation of orange. Or, placing 

 a slip of black or green paper on red paper, so as to 

 shield part of the retina from the red rays, then on 

 removing the slip an image of it is seen on the red 

 ground, the image being of a brighter and more 

 intense red. 



The greatest contrast is obtained when the two 

 colours are complementary to each other. Somewhat 

 prolonged observation of such colours gives rise to a 

 glimmering or lustrous appearance, which is the 

 leading feature of another common advertisement. 



An experiment of Helmholtz furnishes an example 

 of the deception to which our visual judgment is 



liable. He directed two 

 beams of light, one ordinary 

 daylight, and one candle- 

 light, on to a white screen, 



A NEW PARASITIC COPEPOD. 



I LATE BY received from Mr. H. Chad wick, of 

 Manchester, a specimen of Sabella, from the 

 sandy shore at Beaumaris, N.W., which appeared to 

 be infested with Copepoda. They were found at- 

 tached to the gill filaments, to which they clung so 

 tenaciously that it was difficult to remove them for 

 examination without injuring the filament of the 

 worm their host. The worm occurs in large numbers 

 on the beach at Beaumaris, and several specimens 

 taken were all found to be infested with the little 

 Crustacean. 



Microscopical examination clearly shows it to 

 belong to the genus Lichomolgus, family Sap- 

 phirinidse (Thorell), but it differs in many important 

 points from any hitherto known species. I propose 

 to name it Lichomolpus sabella (Fig. 15). 



Its length is about T ' 5 inch, and with even a pocket 

 lens it is readily distinguishable by its long narrow 

 ovisacs and remarkable antennae. The body is 



Fig. 15- — Lichomolpus sahellce Q. 



and interposed an upright rod, so that two shadows 

 were cast on the screen, one in each beam. After 

 adjusting the lights till the shadows were of the same 

 depth, he found that one appeared yellow, namely 

 that cast in the beam of daylight, and the other blue. 

 In this experiment the whole screen is really a pale 

 yellow, being illuminated by a mixture of white light 

 and yellow candle-light, but we accept it as white ; the 

 consequence is that the shadow of the rod in the beam 

 from the candle, which shadow is really pure white 

 or grey since it is illuminated by daylight only, looks 

 blue by comparison. 



Another experiment which depends on our mis- 

 taken visual judgment consists in placing a small strip 

 of grey paper on a brightly coloured paper and 

 covering them with a sheet of tissue paper. The 

 grey strip seen through the tissue paper appears of a 

 complementary colour to the ground colour, and 

 sometimes even more intense. This is a case of 

 contrast between two greys, and the contrast effects 

 are more marked than in the case of more intense 

 colours. 



Fig. 16. — Posterior antenna; 

 of Lichomolpus sabella. 



Fig. 17. — Anterior antenna;. Fig. iS. 



-Pair of Swimming 

 Feet. 



elongated ; the first segment being about half the 

 entire length of the cephalothorax which is of ovate 

 form. The abdomen is composed of five joints : the 

 first joint being in length equal to the remaining 

 four joints, and proportionately broad. In the male, 

 its lower angles are produced into two sharp narrow 

 spines. Rostrum short and beak-shaped. Anterior 

 antennas (Fig. 17) seven-jointed, the two basal joints 

 much longer and broader than the rest, and roundly 

 serrated on the outer margin. All the joints are 

 clothed with strong spinous setae. 



Posterior antenna; (Fig. 16) four-jointed, and very 

 powerful ; the second joint is provided with four small 

 curved hooks placed longitudinally, and the apical 

 segment has four large strong curved hooks, in shape 

 much like shepherds' crooks. 



The posterior foot jaws vary in the two sexes. One 

 of the first four pairs of swimming feet is shown in 

 Fig. 18. The fifth pair are alike in both sexes, and are 

 composed of one joint, with a long and short strong 

 spinous seta at apex. The animal is of a greyish- 

 brown colour. 



