58 



KNOWLEDGE. 



Februarv, 1915 



ZOOLOGY. 



By Professor J. Arthur Thomson, M.A., LL.D. 



CATERPILLARS' SETAE.— It appears that the de- 

 scription of " aerostatic hairs " on the caterpillars of the 

 Gipsy Moth and Nun Moth was mistaken. The globular 

 swellings at the bases of the hairs were supposed to be air 

 reservoirs, facilitating dispersal by the wind. Riley showed 

 some time ago that the swelling does not contain air, but 

 fluid, and that there is a large glandular cell opening into 

 it. It is probable that the fluid is poisonous, and protective 

 against insectivorous birds. 



FORMER CONNECTIONS OF ANTARCTIC CON- 

 TINENT.— In giving an account of the fishes collected by 

 the British Antarctic (" Terra Nova ") Expedition, 1910, 

 Mr. C. Tate Regan, of the British Museum, has taken 

 occasion to examine the evidence in support of the \'ie\v 

 held by many authorities that in the Early Tertiary the 

 Antarctic Continent was connected with Australia and with 

 South America. He comes very definitely to the conclusion 

 that neither the freshwater fishes nor the marine fishes, 

 whether Antarctic or South Temperate, support the theory 

 that Antarctica has connected Australia with South 

 America in Tertiary times. The evidence from other 

 groups of animals seems to Mr. Regan to confirm the con- 

 clusion which he reached from his study of the fishes. 



SHORE MITES.— Professor L. A. L. King's recent 

 observations on some littoral mites on the shore near Millport 

 Biological Station show how much interesting material is 

 available to keen eyes. Thus, as to the feeding of Gamasiis 

 [Eugamasus) immanis, it is noted that the mite plunges its 

 chelate chelicerae into the body of living Oligochaetes, 

 tears out a piece, and sucks it dry. As Michael showed, the 

 male inserts his mandibles into the genital opening of the 

 female, and empties the contents of a spermatic capsule 

 into the vagina. Of Gamasiis (Halolaelaps) glabyiusculus it 

 is noted that it survived complete immersion in water for 

 forty-eight hours. The large red Bdellid (Mo/giis Uttoralis) 

 was seen feeding on a small living Dipteron. The smaller, 

 more vivid, more gregarious Bdella longicornis probably 

 feeds on the Collembolan Antirida maritima, common on 

 the shore. This species of Bdella, as Mr. T. J. Evans, of 

 Sheffield, has also noticed, spins a silken tent in autumn. 



NUMBERING HAIRS.— Evidence of the definiteness of 

 indi\'idualit5' is always interesting. We know of some 

 simple animals which have always, or almost alwa^'s, the 

 same number of cells in particular parts of their body, 

 and in their body as a whole, and Mr. Phineas W. Wliiting 

 has shown the same sort of specificity in the bristles on the 

 back of the Green-bottle Fly (Lucilia sericata). He studied 

 a group of twelve dorsal bristles, and found that the number 

 is hereditary and the distribution hkewise. There may be a 

 few less or more, but only a few. Reduction rarely goes 

 beyond the loss of two bristles in a single fly. Out of five 

 thousand three hundred and sixty-seven flies bred, there was 

 a reduction of 748'5 in the males and of 455-5 bristles in the 

 almost equal number of females. There were two hundred 

 and ten bristles added in the males, and three hundred and 

 forty-three added in the females. 



FREQUENCY OF PARASITES IN FISHES.— The 

 clean and wholesome nature of the flesh of fishes is well 

 known. Its relative freedom from parasites is noteworthy 

 and of practical importance. But the number of parasitic 

 worms found in the intestines, and in other parts of the food- 

 canal, is enormous. Dr. W. Nicoll, one of the foremost 

 helmintliologists, has examined eight hundred and forty-five 

 fishes (one hundred and two different kinds) from around our 

 coasts, and has found eighty-one per cent, with parasites 

 (of over fifty different kinds). Of four hundred and seventy- 

 five fishes from Plymouth, three hundred and eighty (eighty 

 per cent.) were infected : fifty-six per cent, with flukes, 

 forty-four per cent, with tapeworms, forty-eight per cent. 



with tlireadworms, and two per cent, wth Echinorhynchs. 

 Millport fishes yielded the same percentage, St. Andrews 

 fishes eighty-three per cent., and Aberdeen fishes ninety-one 

 per cent. This large incidence of parasites is remarkable : 

 it throws some li,ght on the stern character of the struggle 

 for existence. In most cases, probably, the parasites do 

 little harm unless they reach a host unaccustomed to them. 



THE MAN-OF-WAR INFUSORIAN— A glimpse into 

 the intricacy of things is afforded by E. Penard's description 

 of a ciliated Infusorian, which he found in a marsh near 

 Genev;i, and names Legendrea bellerophoyt. The genus was 

 established by Faur^-Fremiet, but the species, bellerophon, 

 which we have translated " man-of-war," is new. It is 

 from 120-180^ in length, and about a third as broad : 

 it has a slit-like mouth, a horse-shoe-shaped nucleus, a large 

 contractile vesicle, and many other features with which 

 we are familiar in ciliated Tnfusorians. But the remarkable 

 feature is that on each side of the somewhat man-of-war- 

 shaped creature there project about ten papillae at regular 

 intervals, like the guns from a frigate. Each of these 

 papillae bears at its blunt extremity a group of stinging 

 threads, or trichocysts, from which, again, very delicate, 

 probably poisonous filaments can be protruded. Each 

 papilla is like a mitrailleuse, and a very effective weapon. 

 There are trichocysts on other parts of the Infusorian, 

 but they explode only on the projecting papillae. In a very 

 striking way they move or are moved to the bases of the 

 papillae, and accumulate there, " waiting their turn " 

 to pass up, or to be passed up, to the tips of the papillae. 

 When the delicate filament is protruded from the exploded 

 trichocyst a minute viscous drop of poison appears at its 

 ruptured end. The well-armed Infusorian swims slowly, 

 and is carnivorous. It is wont to attack a minute Rotifer 

 called Diplax lyigona. 



ANIMAL HYPNOSIS.— When a Snake becomes a stick, 

 or a Hen lies immobile on the floor with a chalk line in front 

 of its eyes, or a Crayfish stands on its head, or a Ground- 

 beetle (such as Scarites buparius) feigns death on being 

 shaken, we have to deal with animal hypnosis. In a recent 

 investigation Professor Mangold defends the position that 

 animal hypnosis is analogous with human hypnosis, and 

 on the physiological side the resemblance is certainly close. 

 Mangold's definition of animal hypnosis is as follows : 

 A reflex tonic inhibition of locomotion and position-adjust- 

 ment, induced by a sum of afferent stimuli, resulting in a 

 sleep-like state in which there may be great changes in 

 muscular tonus (first increase, and then decrease) and 

 decrease of sensitiveness to many kinds of stimulus, e.g., of 

 a painful sort. One of the many difficulties concerning 

 animal hypnosis is its relative uselessness. It may perhaps 

 be of service when a ground-bird, hotly pursued, squats 

 motionless, or when a mammal " plays 'possum " ; but even 

 this has not been proved to be " hypnosis " in the strict 

 sense, and in most cases among backboned animals the 

 capacity is known only in the laboratory. Among Arthro- 

 pods it is of great service in stick-insects, wliich pass into 

 hypnosis under the stimulus of light, and simulate in their 

 pose the twigs which thev resemble in colour and shape. 

 But in many cases the hypnotic state is readily assumed under 

 various stimuli without any resulting utility being ob\ious. 

 Very interesting is 1he case of the female Galeodes — a fierce 

 and unapproachable creature — wiiich passes into hypnosis 

 when suddenly seized by the smaller and weaker male. 

 It looks as if we had to do with a widespread capacity 

 which persists as a concomitant of an effective nervous 

 constitution, but is only now and again itself brought 

 within the sphere of utility. 



ADAPTATIONS OF THE PLANKTON.— Professor 

 J. Graham Kerr discussed in a recent lecture the 

 adaptations of the drifting animals of the sea. Macro- 

 plankton animals, illustrated by jelly-fishes, pelagic anneUds, 

 like Tomopteris, and Salps, often show transparency, or 

 some coloration, which is a garment of invisibility. In the 



