396 
POPULAR SCIENCE REVIEW. 
the place of branchial ; and atmospheric air is necessary, without which the 
change from tadpole to frog cannot be effected. 
We are all, as children, familiar with spiders' webs. To some they are 
objects of terror, to others of curiosity, and to a few, of attractive pleasure. 
How the little “ curious fly ” is suddenly arrested when his “ gauzy wings ” 
touch that fatal barrier ! There is no escape, and out rushes webspinner to 
his dinner. Our friend Mr. Richard Beck has lately paid some attention to 
the nature of the viscid lines which thus entrap unwary insects, and read a 
a paper before the Microscopical Society lately, upon that subject. The 
beautiful regularly-formed webs of the geometric spiders are dotted, except in 
the closely-packed central fibres, with minute drops, which Mr. Blackwall 
has calculated the spider to produce at the rate of 200,000 in an hour. Mr. 
Beck, watching the little architect with a lens, observed that when the thin 
web left the spinnaret, although viscid, no dots were apparent. More close 
examination with the microscope rewarded the observer with a sight of the 
changes which the viscid threads underwent. At first slightly thicker than 
ungummed threads, the viscid secretion soon began to form undulations, and 
eventually separated, forming globules, by molecular attraction, at very regular 
and very minute intervals. Hence, while the wonder of the construction is 
in no way diminished, the incredible number of these little globules is 
accounted for by the supervention of a physical law, after the sufficiently 
marvellous organic law lias fulfilled its purpose. 
During some microscopic examinations, Mr. Attfield has discovered some 
new species of acari, which feed upon extract of nux vomica. In order to 
ascertain whether these curious little insects, which greatly resemble cheese- 
mites, really eat the strychnine, or only lived upon the starchy matter of the 
extract, some were collected and placed in two cells, one of which contained 
powdered strychnine, the other being empty. The acari in the empty cell 
were starved to death in a few days, whilst those with the strychnine were as 
lively as ever. Other new species of acari were fed upon other poisonous 
extracts. Those from colocynth thrived equally well on strychnia, colocynth, 
or cheese, but cheese-mites ivere poisoned when fed upon strychnine. 
But if spiders, with all the wonders of their constructive skill, are, after 
all, but doubtful favourites, there can be no doubt concerning the attraction 
which the gay and careless butterflies possess for all ages, and for the scientific 
and the unscientific alike. The delight caused by the magnificence of their 
wings as they flit about in the sunshine only gives place to wonder when 
those wings are placed piecemeal under the searching microscope, and the 
innumerable feathers of which they are composed, far outrivalling in 
number and brilliancy those of the paradise-bird, gives one a feeling of 
revelling in the richness and prodigality of bounteous Nature. It would be 
more proper, in scientific language, to call them scales than feathers, for 
scales they really are, as the term Lepidoptera, or scale-wings, indicates. In 
the “ Annales des Sciences Naturelles” is an article * on the wings of Lepi- 
cloptera, by Bernard Deschamps, from which it appears that these scales are 
composed generally of two or three membranes placed one above the other, 
* Translated by Mr. A. G. Latham, and read before the Microscopical Sec- 
tion of the Philosophical Society of Manchester. 
