October, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



553 



struggle for existence among these small organisms 

 takes a character of almost human unsociableness. 

 The smallest animals present themselves in the light of 

 genuine monsters. Their rapid motions, evoked by no 



Mow a Fly Looks in the Bioscope. 



external cause, reveal their muscular jjower. The en- 

 vironment in which they live appears through the ap- 

 paratus like a landscape with strange and fantastic 

 forms, made attractive by multi-coloured plants of 

 which the transparent structure carries our thoughts 

 into other worlds or toward the remote epochs of the 

 prehistoric ages of our planet. Ants furnish a particu- 

 larly interesting field for observation, and spiders are 

 no less curious objects for observation. The bioscope 

 is also valuable for scrutinising the life of aquatic 

 animals through the sides of an aquarium, or even in 

 their natural element. It permits of studying bodies 

 submitted to wry high temperatures, electric dis- 

 charg-cs, \'c. It may be added that in the domain of 



A Spider ut \Vorl<. 



medicine it renders possible the obsiiv alion. under a 

 strong magnification, of dimly-lighted cavities (the 

 larynx, ears, &c.), and of formulating a diagnosis in 

 many cases that have up to the present been doubtful. 

 The apparatus is exlrenielv simple, and is [Movided 



with a camera lucida to permit of the drawing of the 

 objects observed. It consists of a tube with a rack 

 provided internally with a system of achromatic objec- 

 tives perfectly free from spherical aberration, and with 



Spider Attackinj; the Fly. 



a wide field eye-piece. The apparatus is also provided 

 vv ith a system of mensuration and various arrangements 

 for supporting diaphragms. At a distance of 19.9 

 inches, the bioscope has a magnifying power of more 

 than 12 diameters, say of 144 times the surface. 



The Study of Heredity. 



(Continued from page 5 j t . y 



The 253 hybrids thus obtained yielded, on self- 

 fertilisation, 8,023 seeds, of which 6,022 were yellow 

 and 2,001 green, the ratio beingf 3.01 to i. Plants 

 raised from the green seeds produced only green seeds 

 in subsequent generations; that is, the " extracted re- 

 cessives " are a pure race identical with the original 

 recessive parental form. From a sample sowing of the 

 yellow seeds Mendel raised 519 plants; of these ibb 

 yielded exclusively yellow seeds, while 353 yielded 

 yellow and green seeds in the proportion of 3 to i. 

 The former are pure dominants, and continued to breed 

 true; the latter are hybrids of the same nature as those 

 of the first filial generation, and it will be seen that the 

 pure dominants are to the hybrid (apparent dominants) 

 in the proportion of I to 2. The latter continue to split 

 in subsequent generations in the proportions of i pure 

 vellow : 2 hvbrid vellow : 1 pure grei-n ; or i DD : 

 2 I)R : 1 RR. 



Mendel worked with considerable numbers of in- 

 dividuals, and, although in individual cases, when the 

 inunbers are small, the ratio.s may not be obtained so 

 exactly as in the case cited, yet it is impossible to doubt 

 the general accuracy of the ratios, when an average 

 of the results is taken. The purity of the pure 

 dominants and pure recessives resulting from the self- 

 fertilisation of cross-breds was tested by Mendel in 

 some cases as far as the 6th generation. 



i'o explain these constantly recurring ratios, Mendel 

 sug-g-ested that in peas each pure race produces egg 



