474 



SCIENTIFIC NEAVS. 



[May iS, if 



The machine is self-exciting under all conditions of 

 atmosphere, owing probably to each plate being influ- 

 enced by, and influencing in turn its neighbour, hence 

 ihere is the minimum surface for leakage. When excited 

 the direction of the current never changes; this circum- 

 stance is due probably to the circuit of the metallic 

 sectors and the make-and-break contacts always being 

 closed, while the combs and the external circuit are sup- 

 plemental, and for external use only. The quantity of 

 electricity is very large and the potential high. When 

 suitably arranged, the length of spark produced is equal 

 to nearly the radius of the disc. I have made them from 

 2 in. to 7 ft. in diameter, with equally satisfactory results. 



BRADFORD NATURALISTS' SOCIETY. 

 At the fortnightly meeting, held on April 23rd, the Presi- 

 dent, Mr. J. Clayton, in the chair, Mr. W. D. Roebuck, 

 F.L.S., delivered a lecture on "The Genus Arion." 

 After referring to the distinctions which separated this 

 genus from the other genera of slugs — viz., that in them 

 the shell was rudimentary, the shield granulated and not 

 striated, the breathing-hole at or before the middle of 

 the shield, and the back devoid of keel — he proceeded to 

 ^peak of the species which compose it, and how they 

 may be distinguished from each other. He stated that 

 all existing English text-books were unreliable, the 

 various species being much confused in them. The 

 researches of Mr. Taylor and himself during the past 

 few years, aided as they were by the anatomical skill of 

 Mr. Charles Ashford, of Christchurch, Hants, and the 

 kindness of innumerable conchologists in all parts of the 

 country in furnishing specimens for study, had suc- 

 ceeded in establishing, on anatomical and therefore 

 satisfactory grounds, the existence of four species as 

 British, in lieu of the three described by Dr. Jeffrey's 

 classical book. The four British species of Arion are 

 A. ater, A. sitbfuscus, A. hortcnsis, and A. bourguignati. 

 Of these the second and the fourth are quite new as 

 British, and it is only A. ater and A. hortcnsis which 

 survive of Dr. Jeffrey's three species. His third species, 

 A. flavits is a mythical creature — a mere name, com- 

 pounded of juvenile examples of the other species, 

 especially of A. ater and A. subfusciis. The diagnostic 

 characters of each species were then entered upon, and 

 notes on their habits, food and life history, their colour 

 and variation were given. Arion ater, which in its most 

 common form is so well known as the " Black Slug," is 

 the largest species of the genus, extremely variable in 

 shade, being found of nearly all colours from intense 

 black, deep brown, warm brown, ochre, yellow red, 

 slate, etc., to creamy and sometimes nearly pure white. 

 It is very distinguishable from the others, not only from 

 its large size and its uniformity of colouring as an indi- 

 vidual, but also by its timidity and its being the only 

 one which can be made to contract into a globular or 

 hemispherical shape when at rest, the others being 

 always more or less cylindrical when in a state of con- 

 traction. This species is very widely distributed and 

 common, and ascends to the summits of our highest 

 hills. It feeds mostly upon vegetable matters, but is 

 omnivorous and often carnivcrous in its diet. Its period 

 of life is about a year, from one autumn to another. An 

 abstract of Dr. Simroth's observations on its colouring 

 matter was given. He finds that there are only two 

 colouring matters, a black pigment and a red pigment, 

 which, mingled in varying proportion, produce all the 

 "varying shades of colour exhibited by the species. He 



finds, further, that relative development of red or black 

 pigment depends upon the temperature at the season of 

 growth, and that each colour is protective, that the black 

 fortifies the constitution against the extremes of heat and 

 cold, and that the red, when developed to an extent 

 which makes the animal conspicuous, makes it also so 

 repulsive in taste and smell that birds will not touch the 

 brilliant red Arions which tourists know so well in the 

 Black Forest. A. subfnscus was illustrated by a fine 

 living specimen sent by Mr. Ashford. It is a middle- 

 sized species, less than A. ater, but larger than the 

 others. It is a striped or banded species and has a very 

 limited range of variation, being nearly always of a 

 tawny yellow, more or less inclined to grey on one hand 

 or to orange yellow on the other. It is in diet more 

 particularly a fungus-eater, preferring the large fleshy 

 Agaries and Boleti. It is not so common as the other 

 species, but equally widely distributed. The third 

 species mentioned was A. hortensis, or the " Garden 

 Slug," a most appropriate name, for it is not usually 

 found away from cultivated land and human habitations. 

 In gardens it is very destructive, and most insidious in 

 its ravages. It is also very thick skinned and difficult 

 to crush underfoot. It is readily distinguished from our 

 other species by the sole of its foot (that is, the whole 

 under surface of the body), being always more or less 

 yellow, often brilliant orange, while in the other species 

 it is white. The fourth and last species mentioned, A. 

 bourguignati, has always hitherto been confounded with 

 A. hortensis or regarded as a variety of that species, from 

 which, however, it is abundantly distinct both internally 

 and externally. Of about the same size, it is stouter 

 and broader, not so slender and cylindrical, always paler 

 and whiter in appearance, and never with yellow on 

 the footsole, which is always distinctly white. Its 

 habitat is different, as it lives more in the open country, 

 and is equally widely and commonly distributed. 



ANTHROPOLOGICAL INSTITUTION. 

 Ax the meeting held on April 24th, two interesting 

 papers were read by Dr. Venn, F.R.S., on " Recent 

 Anthropometry at Cambridge," and by the President, 

 Francis Galton, Esq., on the "Head-growth of Cambridge 

 Students." Both papers dealt with experiments made in 

 the direction of measuring the cubic contents of brain in 

 specially selected classes. At South Kensington the 

 heads of over 9,000 persons were measured, the method 

 adopted being to multiply the maximum breadth, taken 

 from ear to ear, by the maximum length from the frontal 

 sinus to the back of the occiput, and multiply this num- 

 ber into the height of the arch of the head above the 

 orbits of the ej'es. The South Kensington group was 

 chiefly selected from a homogeneous class of what may 

 be called the " upper professional classes, well fed, well 

 clothed, and the progeny of parents who had enjoyed 

 similar advantages." Tabulated statements of the statis- 

 tics so arrived at were shown at the meeting, and with 

 these were compared the recently taken Cambridge 

 University statistics of head-measurement. The rela- 

 tive powers of " pull," " squeeze," breathing power, and 

 the height and weight were also compared, with a result 

 strongly in favour of Cambridge men, on the whole, as 

 compared with the South Kensington group, the figures 

 being as follows : 



Height. Pull. Squeeze. , Breadth. Weight. 



Cambridge 689 83 87-5 254 153-6 



S. Kensington 67-9 74 85 ...._ 219 143 



These figures point to the high physical condition of the 



