126 



♦ KNOW^LEDGE ♦ 



[Aug. 15, 1884. 



wild flowers as well as those of indoor growth, does not 

 behave in that way. Most probably the mouths of all the 

 species are constructed upon a closely similar pattern : but 

 it is the greenhouse plague that is figured here. The 

 mouth parts are very ditticult to make a complete display 

 of, but, capable of pr jection in advance of the " short-beak " 

 of various writers, comes the long, flexible rostrum shown 

 in Fig. 2. The writer thiuks it is furnished with two or 

 three very slender seta*, but leaves this for further inquiry. 

 This organ, when at rest, lies in the middle of the "short 

 beak," and unless projected forward is easily confounded 

 with it. It seems capable of a lateral motion. All the 

 mouth-organs commence at the lower part of the head. 

 The "short beak" extends to the first coxa>, and the rostrum 

 can be thrust beyond it. Fig. 3 is a maxillary palp, and 

 Fig. 4 a labial one. Two slender " horny, setiform man- 

 dibles," as figured by Westwood, have sharp and probably 

 piercing tips. In one mounted specimen two fine rapier- 

 shaped instruments are thrust forward in advance of the 

 rostrum, only the tip of which projects a little beyond the 

 " short beak." Are they maxillie ? To see the rostrum, 

 which has escaped the notice of so many observers, the 

 head of the insect should be pushed ofi' by pressing it 

 forwards with a fine needle. This will probably cause the 

 rostrum and some other parts to be seen extending hack- 

 wards. If the ^rst attempt is not successful, the process 

 should be repeated till the end is accomplished. The larva 

 and pupa much resemble the perfect insect, but they are 

 yellow and very transparent. They reach the imago state 

 through a succession of moultings. Their mouth organs 

 seem like those of the adult, and if a few of the larger ones 

 are mounted in thin Canada balsam some are pretty sure 

 to exhibit the rostrum and some of the other mouth parts. 

 In the head of the pupa several long muscular bands to 

 work the mouth-parta are very interesting to view with 

 powers of 200 and upwards. The mandibles and maxillaj 

 are of transparent glassy aspect ; the rostrum is brown 

 and chitinous, deepening in tint towards the tip. When 

 the whole of this organ is seen, it corresponds to a gun 

 with the barrel at an angle with the much curved stock. 

 Not having succeeded in displaying the whole of the mouth 

 organs in their natural position, naming them is uncertain, 

 except as regards the rostrum, which clearly belongs to 

 the Haustellate or Sucking insects, and not to the Mandi- 

 bulate or Biting ones. 



Their modes of doing mischief are twofold. Firstly, by 

 piercing leaves or other objects of attack, and sucking out 

 the plant juices; and, in the second place, by depositing 

 their excrement in the form of blapk globules as stiti' as tar. 

 Vines and fuchsias are favourite objects of attack. The 

 adults seem to like the upper side of the leaves best, and 

 the little yellow babies and juveniles aS'ect the under side. 

 The latter are so transparent as readily to show the con- 

 tents of their intestines, and it is curious how soon their 

 digestive processes turn the green leaf matter into the 

 black mess which kills the part it is deposited upon. The 

 insects may be seen moving about with balls of this stufi" at 

 the end of their tails. The adults, when disturbed at their 

 work on the leaves, never use their wings in order to 

 escape, but can run pretty quickly. 



When they get into cucumber or melon frames they are 

 very destructive, and troublesome to get rid of. They can 

 stand a wonderful lot of tobacco-smoking, and most of the 

 vaunted insecticides are of little use. With pot-plants, the 

 best thing is to wash them off with yellow soap, or, better 

 still, with Gishurst Compound, which is a sulphur soap. 



The damage done by these little pests is always serious 

 It they get into any frame or house, and the species that 

 attacks farm crops is terribly injurious. Curtis quotes 



Halliday to the effect that in 180.5 they destroyed one- 

 third of the wheat crop in the richest part of Piedmont, 

 and in the same year they caused similar losses to the 

 British farmer. Olives, peaches, melons, and potatoes 

 are assailed by some of the tribe. In attacking wheat, 

 rye, &c., they are found between the interior valve of the 

 corolla and the grain, causing; the latter to shrink, or be 

 pungled, as they call it in Suflblk. In one case an orange- 

 coloured powder was noticed in the grains that had been 

 attacked, and was taken for the insect's excrement, which 

 is not at all like it. Probably the yellow powder was one 

 of the rust fungi.* 



In preparing these olyects for the microscope some should 

 be mounted whole in thin balsam. To display the wings, 

 the abdomen should be pushed off, and the head, thorax, 

 and wings treated in the same way. What to do with the 

 head has already been explained. The feet do not exhibit 

 the bladder-like endings at all well in balsam. Probably 

 some fluid would do better, but they are very diflicult to 

 make out. Before balsaming the whole insect, it is well 

 to soak it for an hour or two in a drop of carbolic acid, 

 which helps to make the balsam penetrate, and adds to the 

 transparency of the preparation. 



THE CAPTURE THEORY OF COMETS. 



By PiicHARD A. Proctor. 



{Continued from 'page 112.) 



ARRIVED at Jupiter's distance from the sun, the 

 meteor flight from interstellar space will have a 

 velocity of about eleven miles per second. Now let us 

 inquire what its velocity must be reduced to in order that 

 it may thenceforth be compelled to travel in a circle around 

 the sun. As a matter of fact, all the members of Jupiter's 

 comet-family travel in orbits whose remotest parts are near 

 Jupiter's orbit, and to give a comet riuch an orbit as one of 

 these much more must be done in the way of reducing 

 velocity than is necessary merely to make the meteor flight 

 from outer space travel thenceforth in a circle at Jupiter's 

 mean distance. We are taking, in fact, a very unfavour- 

 able case for our argument Still, the velocity must be 

 reduced, even in this case, by nearly three-tenths, or by 

 more than three miles per second. 



Now Jupiter's power to withdraw velocity from a body 

 in his neighbourhood is measured by his power to impart 

 velocity. In fact, both processes are but different forms 

 of the same kind of work. Precisely as we say that the 

 sun can communicate a velocity of three hundred and 

 eighty-two miles per second to a body approaching him 

 from interstellar distances, and that therefore the sun can 

 withdraw such velocity from a body leaving his surface at 

 that rate, and eventually bring such a body to rest out 

 yonder in interstellar space, so can we make a corresponding 

 statement for any planet, ^Tupiter or Saturn, the Earth, 

 our Moon, and even for the least of all, the asteroidal family 

 (supposing only the mass and size known). In the case of 

 Jupiter, for instance, we find that the utmost velocity he 

 can impart to a body reaching him from external space is 

 about thirty-six miles per second. That, at least, is the 

 velocity with which such a body would reach the visible 

 surface of the planet What the velocity might be with 

 which the real surface, far down below the visible envelope 

 of clouds, would be reached, we do not know, — not knowing 

 where that surface lies. In the case of oui- own earth, the 



* Dr. Cooke's " Microscopic Fungi " is a good popular introduc- 

 tion to the study of rast, smut, Ac. 



