276 



KNOWLEDGE. 



July, 1913. 



a violet colour. The colour, shining through the brownish 

 integument, makes the grub most effectively harmonious with 

 the colour of the stamens amid which it works. 



relaxation of the muscles mentioned above and — in Dioduns 

 and Tetrodons, at least — by the action of the ventral body 

 muscles, which are adapted to this purpose. 



DEATH-FEIGNING IN I N SECTS. — This very 

 interesting reaction has been carefully studied by Professors 

 H. H. P. Severin and H. C. Severin with especial reference to 

 Belostoma and Nepa, two water-bugs. The death-feigning 

 positions are characteristic and definite, unlike those of the 

 dead insects. The average duration of the " feint " in 

 Belostoma was eight hours, and it is proved that the length 

 is affected considerably by the external conditions of drought 

 and illumination. The death-feint continues even when the 

 head of Belostoma is cut off, and decapitated specimens will 

 often swim freely after arousing from the feint. Both the 

 water-bugs studied are very sensitive to contact stimuli, and 

 in both species there is a marked propensity to cling together 

 and form clusters. The investigators do not think that there 

 is any conscious effort to deceive enemies through the death- 

 feigning. The act is non-intelligent and wholly instinctive. 



FECUNDITY OF THE PO M AC E-F L Y — In some 

 Lepidoptera the reproductivity of the adult female depends 

 wholly on the nutritive conditions of the larva. In other cases 

 like the blow-fly, almost everything depends on the nutrition, 

 of the adult. In the pomace-fly, Drosophila ampelophila, 

 the nutritive conditions of any period have their effect on the 

 number of eggs produced and laid by the female fly. This 

 has been shown very clearly by Emile Guy6not. Immature 

 flies fed on potato become mature in seven to thirteen days 

 and lay an egg per diem ; but those fed on potato and 

 yeast become mature in four to five days at the most and lay 

 ten to fifteen eggs per diem to begin with, and twenty to 

 twenty-five later on. Mature females fed on yeast while 

 immature, but afterwards placed on potato diet, begin 

 to lay a day after their emergence, and they exhaust 

 themselves towards the end of the third day, thereafter pro- 

 ducing only one or two in a day. But their sisters, kept on 

 potato and yeast, continue producing a regular twenty to 

 twenty-seven eggs every day. Thus the influence of nutrition 

 on fecundity is made very clear. 



CAVE SPIDERS. — Louis Fage has made a study of a 

 family of spiders, Leptonetidae, whose members are almost all 

 restricted to caves and grottos. There are some interesting 

 features. Thus it is not usual to find more than one species in 

 one cave, as if there were some intolerance of strangers in the 

 darkness. The webs spread among the stalactites and 

 roughnesses are very large and delicate. The spinners move 

 very slowly. If there is the least disturbance they either 

 quicken their pace or play possum with their limbs laid along 

 their body. In most spiders the males are found only at 

 certain seasons, but in the uniformity of the caves they are 

 found all the year round. The reproduction is not punctuated. 

 In the few cases where the eggs are known, the interesting 

 feature is that each cocoon contains very few, but these are 

 large. In some cases there are only two eggs ; in Telema 

 tenella there is only one in each cocoon. It is two-fifths of 

 a millimetre in diameter and the whole spider is only about a 

 millimetre. The adaptation here is that the young spider is 

 vigorous when hatched. It has had the advantage of a big 

 legacy of yolk. 



INFLATION IN FISHES.— For a very long time it has 

 been known that many globe-fishes and their relatives have 

 the power of inflating themselves and floating on the surface. 

 Nils Rosen has been studying the mechanism of the inflation. 

 It is the air-sac that is filled — by swallowing movements. The 

 air is kept in by means of circular muscles in the wall of the 

 gullet and by a valve, or by means of a special closing muscle. 

 As a result, the body is like a football, and if there are spines 

 they stand out. The Diodons turn upside down and are 

 driven about on the surface of the sea by waves and currents. 

 It is a protective adaptation. The air-sac is emptied by the 



GIZZARD OF BEETLES AND ORTHOPTERA.— It has 

 been too hastily assumed that the gizzard of insects, like the 

 water-beetle and the cricket, functions as a mill for grinding 

 up hard parts. Willy Ramme finds that it is mainly an organ 

 which allows some of the digestive juice of the mid-gut to 

 pass through into the crop, and which works up a sort of mash 

 of food and digestive juice. In all the insects studied the 

 digestive juice of the mid-gut was found in the gizzard (or 

 proventriculus) and in the crop. In Dytiscus the indigestible 

 parts, e.g., chitinous fragments, are kept back by the proven- 

 triculus and passed out again. In Orthoptera the indigestible 

 debris passes on through the intestine. 



FUNGUS GROWING ON HAIR OF ECHIDNA.— 

 Karl Toldt reports the occurrence of an entirely new hair- 

 fungus which he found spreading its hyphae over and in the 

 cortical substance of the bristle-like hairs of Zaglossus 

 (Proechidna) bruijni from New Guinea. He suggests that 

 an examination of the hairs of the rarer mammals would 

 reveal the existence of some new and interesting Fungi. 



HOW MUCH DOES A STARFISH SEE ?— At the end 

 of each arm in the common starfish there is a little red eye. 

 It is sheltered at the base of the terminal tube-foot, which has 

 become altogether sensory. The eye or eye-cushion shows 

 numerous little cups, each closed by a lens, lined by red rod- 

 like sensory cells, clothed externally by supporting cells, and 

 containing a transparent watery substance. Hellmuth 

 Plessner has recently made a number of experiments at 

 Heligoland in order to discover how much a starfish sees with 

 these " eyes," or eye-spots. The answer is: Not very much. 

 It does not form an image nor does it perceive a moving 

 object. But it has considerable sensitiveness in distinguishing 

 different degrees of light and shade. Even the skin of the 

 starfish is responsive to differences of illumination in the 

 immediate vicinity, but by means of its " eyes " the starfish 

 becomes aware of distant illumination that differs, either 

 positively or negatively, from that of the immediately 

 surrounding area. 



FERTILISATION AND CONJ UGATION— When an 

 egg is fertilised there is an intimate and orderly union of the 

 nuclear elements of the egg-cell with those of the sperm-cell. 

 The number of chromosomes in each has been reduced during 

 the ripening process to half the number which is normal for 

 the species in question. Thus in fertilisation there is a 

 restoration of the normal number. It must also be admitted 

 that the spermatozoon brings with it an extremely minute 

 quantity of cytoplasm, which probably has some significance. 

 It is also well known that the spermatozoon introduces into 

 the egg-cell a centrosome, which divides into two and plays an 

 important role in the subsequent segmentation. The fertilising 

 spermatozoon keeps the egg from dying, as in all ordinary 

 circumstances it would otherwise do, and gives it some 

 initiative to development. In certain cases (of artificial 

 parthenogenesis) this part of the sperm's role can be replaced 

 by chemical or physical stimulus. But the other main role — 

 the mingling of two inheritances — is something quite apart 

 and more distinctively vital. Now it is interesting to find that 

 the careful experiments made by Professor H. S. Jennings on 

 conjugation in Paramoecium, the slipper-animalcule, all point 

 to the conclusion that conjugation does not effect any 

 rejuvenescence, its meaning being rather to secure biparental 

 inheritance, which often means variation. When the conditions 

 of life are untoward, conjugation is apt to occur, and it may 

 be followed by new combinations of qualities, some of which 

 are suited to the altered conditions of life. In those infusorians 

 conjugation implies a loss of vigour, but it promotes variations 

 some of which pay by securing survival. 



