240 



KNOWLEDGE. 



June. 1911. 



permitting the light to get through the second prism. The 

 rotation is only produced where the refractive index of the 

 vapour is very high, namely in the neighbourhood of the 

 sodium flames. If the sodium vapour be very dense, the 

 beam of yellow light will be twisted round and round many 

 times. The light examined in the spectroscope is shown to 

 consist of a number of light and dark spaces on each side of 

 the " D " lines. 'each line representing a rotation of the beam 

 through 180'. In some cases the direction of the rotation of 

 the plane of polarization is opposite to that of other wave- 

 lengths, which Professor Wood has shown by means of a most 

 ingenious double quarts prism of right and left handed 

 rotation. The rotation of the plane of polarization of the light 

 in the neighbourhood of the absorption bands of iodine was 

 shown : the little monochromatic elements in the spectrum are 

 selected out and give a line spectrum. Professor Wood 

 referred finally to the reflecting power of vapours which if the 

 absorbing power is great sho\ild also be. great. He has been 

 successful in obtaining reflection from mercury vapour under 

 high pressure in quartz vessels when illuminated by ultra- 

 violet light. 



ZOOLOGY. 



Hv Professor J. .Xrthur Thomson. M.A. 



ARTIFICIAL PAKTHKNOGKNESIS.— It is now reported 

 that the eggs of frogs and toads may be got to develop wdthout 

 fertilisation. Bataillou takes a piece of a string ot toad's 

 spawn with as little jelly as possible, puts it in a dry dish, 

 bathes it with a little blood, and makes minute punctures in 

 the eggs. They segment " magnificently," and the frog's blood 

 works as well as the toad's, and better than the spermatozoa 

 of the frog I Dehorne has made a careful study of a frog 

 larva parthenogenetically produced which lived for eight days. 

 The cells of its body had. as theory would lead one to expect, 

 only six chromosomes in their nuclei. — half the normal number. 



.\ CL'KIOL'S HABIT. — Erik Rergstrom calls attention to 

 a puzzling piece of behaviour which he has noticed in 

 reindeers at the time of antler-growth. With some difliculty 

 they frequently bring the tip of the antler into contact with 

 the hoof-gland, and the result is that the tip is smeared with 

 the viscid secretion. Hut why ? 



KINGS ON FRESHWATER MUSSELS.— There is some 

 peculiar satisfaction in observing the organic registration of 

 growth-periods, — so familiar in the rings of wood on the sawn 

 tree-stem. It is strikiiig. too, to read back to a peculiar line 

 where there seems to have been no summer wood formed, and 

 to find, on consulting the meteorological calendar, that this 

 corresponds to what was called '' the black year," when there 

 was no summer. So from the scales of a fish, or from its 

 otoliths, or even from some of its bones, one may read its age 

 with security, corroborating one index by another. According 

 to Malloch one can tell from the salmon's scales whether it has 

 spawned or not. and more besides. A case that has always 

 interested us. becau,se of the great variety in the succession, 

 is that of the rings on freshwater mussels, but we are not 

 aware of precise observations on the subject. In a recent 

 paper Israel points out that two rings are sometimes laid down 

 in one year. 



FLIES .AND ERGOT. — We have heard much in recent 

 years of the part that flies play in disseminating disease-germs 

 — typhus-bacilli, sleeping sickness Trypanosomes, and many 

 others. It is interesting to notice that L. Mercier has found 

 that a common summer fly. Sciara tkomac, carries about the 

 spores of Claviccps which causes ergot on rye-grass. The 

 conidia of the Claviccps were abundant in the food-canal of 

 the flv and did not seem to be affected. There were also 

 others on the setae of the body. The flies frequent rve-grass, 

 but experimental proof that they infect healthy plants with 

 Claviccps has not yet been furnished. 



SPIDERS AND MOSOUITOES. — N. Leon gives an 

 accoimt of the formidable numbers of Mostjuitoes in Roumania 

 along the shores of the Danube. E%ery here and there, in 

 some tracts, one sees the canopied al fresco beds where the 

 fishermen sleep, or try to sleep. Equally characteristic is the 

 astonishing abundance of spiders' webs which sometimes 

 cover the trees with a thick veil. These are of no slight 

 importance in imposing some check on the multiplication of 

 the mosquitoes. As things are, the plague is sometimes 

 terrif\ing. but it would be much worse without the spiders. 



HVDRACTINIA AND HllKMlT CKAH.— Prof. Seitaro 

 Goto, of Tokyo, describes two species of Hydractiiiia which 

 occur in Japanese waters in association with a hermit crab 

 (Etipagunis coiistaiisK and form shells of their own entirely 

 composed of a chitinous framework. In most specimens there 

 is apparently no basis of gastropod shell, as is the casein most 

 other known species of Hydractiiiia. The skeleton of one of 

 the species (//. spiralis sp. n.) is totally devoid of spines, and 

 its substance is very thin and papery, while that of the other 

 IH. soilalis Stimpson) is richly armed with large spines, which 

 arc conical when small, but irregular in shape and branching 

 when large. The skeletons of this species are rather common 

 and are sold in a dry state under the name " Igaguri-gai," or 

 " Chestnut-burr shell." 



SPECIFICITY.— The late Mr. George Sim. of Aberdeen, 

 author of " The Vertebrate F~auna of Dee," was wont to say 

 that he could identify any British fish from a square inch of 

 its skin. In other words, the scales of each species have 

 distinctive peculiarities. They show specificity. And the 

 more we know of the members of well-defined species the 

 more we become convinced of the unity of the organism. 

 Distinctiveness penetrates into every hole and corner. A 

 striking illustration has recently been given by W. J. Loginoff, 

 who shows that the ciliated cells hning the windpipe of horse, 

 ox, sheep, and so on, are so distinctive in each case that it is 

 not very difficult to tell from a preparation what animal it 

 came from. 



By Wii.i'RED Mark Wehh. F.L.S. 



THE FAIRY SHRIMP.— It is interesting to record that 

 Mr. B. J. Hunter has recently found examples of the F'airy 

 Shrimp in ponds near Pewsey in Wiltshire. Commenting on 

 the fact mentioned by Mr. Pyman (" Knowledge," Volume 



XXXIII, page 251) that the styles projecting from the telson of 

 the female were usually broken, Mr. Hunter says that he 

 noticed "a small animal that seemed to have a bivalve shell, 

 which propelled itself rapidly through the water by means of 

 its feet, attached itself to these styles and ate them, the 

 shrimp appearing not to notice it until it had reached quite a 

 distance when, by means of a powerful jerk, it was thrown off." 



FLEAS AND PLAGUE.— In " Knowledge," Volume 



XXXIV, page 12, Mr. Grew, in deahng with the question as 

 to whether there was much likelihood of fleas carrying plague 

 in Europe, gave the generally accepted opinion that the 

 luiropean rat flea. Ccratophyllus fasciatiis, will not feed 

 on man except when starving. Quite recently a number of 

 experiments have been made at the Lister Institute of 

 Preventive Medicine by L")r. Harriette Chick and Dr. C. J. 

 Martin, which have been published in The Journal of Hygiene 

 for .^pril Sth, and Dr. Chick has kindly sent us a reprint 

 from which we learn that Ccratophyllus fasciatus, when 

 hungry, will attach itself to man with great readiness. A 

 hundred and sixty-one experiments were made, of which we 

 describe one. A rat was removed from a flea-breeding cage, 

 and four days later the hand and arm of a number of persons 

 were placed in the cage at difl'erent times during the day for 

 two minutes. In one instance as man\- as eighteen fleas 

 jumped upon the arm, many of which could be felt at once to 

 bite vigorously. 



