454 



NATURE 



\Scft. 7, 1S82 



extreme tenuity, others were dense and bright, hiding the stars 

 over which they passed. The sky in the end was covered with 

 a light haze, which condensed into a cloud canopy. No pris- 

 matic colours were visible, streamers, beams, and rays through- 

 out being alike of a pure white light, though greatly luminous, 

 so as to retain di. tinctive individuality in the face of brilliant 

 moonlight. Thursday, early morn, sun shining through a hazy 

 -,ky, wind light from the south; 9 a.m., overcast; II a.m., 

 rainfall set in. Continuous all the day. Sharp fall of baro- 

 meter. Thermometer mid-day, 65, wind inclined to back to the 

 eastward. Considering that the vernal and autumnal equinoxes 

 are the usual periods of auroral activity, and that there is yet a 

 month to the 21st of September, an instance, now of auroral 

 energy is somewhat out of the usual course of things. The 

 equinoctial gales, yet earlier, set in with much rigour. Perhaps, 

 as everything has a meaning, these phenomena presage the kind 

 of weather which is to rule the autumn. Scarcely a summer 

 bird remains save the swallow and martin. The swift left early. - 

 A solitary bird or a pair was observed, however, evening by 

 evening up to the 28th to return to the nesting place of the tribe, 

 as loth to leave the English home. To day (Friday) continuous 

 rain, which has prevailed all the night. Mid-day, thermometer 

 64 ; barometer 20/3 ; set of wind southerly. X. 



Worcester, September 1 



Habits of Spiders 



\ r OUR correspondent, Mr. Frank Kowbotham, in his letter on 

 the " Habits of Spiders " (vol. xxvi. p. 386), gives it as his 

 opinion that a spider shakes the web from a desire "to effect 

 concealment when it feels danger is near." I am inclined to 

 think it does so from a feeling of anger. During a long resi- 

 dence in the tropics, I often amused myself irritating spiders 

 and watching their conduct. I noticed that they generally seized 

 the web and shook it up and down in the manner described by 

 your correspondent, but some of the spiders were of so great a 

 size as to render concealment by such a manoeuvre quite hopeless, 

 and I attributed their behaviour to other motives. They appeared 

 to me more to resemble angry monkeys than anything else. I 

 have not unfrequently seen the latter when annoyed jumping up 

 and down on all fours with their tails erect in the air, or if con- 

 fined in a cage seize the bars bp their hands and feet and shake 

 them as the spiders did their webs. W. J. C. 



Torquay, August 30 



THE RESPIRATORY MOVEMENTS OF 

 INSECTS 



THE respiratory movements of some of the larger 

 insects are quite apparent, and have been described 

 by various observers. A German naturalist, Herr Rathke, 

 published in 1861 a memoir in which he compared those 

 movements, observed with the naked eye and a magni- 

 fying glass, in insects of all the principal types. 



According to M. Plateau (who has lately studied the 

 subject, and has made a preliminary communication of 

 his results to the Belgian Academy), though Rathke's 

 memoir is very remarkable, he overlooked many details, 

 and fell into sundry errors, owing to the difficulty of the 

 inquiry. 



Haussmann (1S03) suggested a method of indicating 

 the movements of dilatation and contraction of an insect's 

 abdomen, by oscillations of a liquid column ; but he 

 recognised that it would apply only to articulata of large 

 size, and it seems incapable of yielding very exact 

 results. 



M. Girard (1873) proposed encasing the insect's abdo- 

 men with a thin envelope of caoutchouc having a style 

 attached which would inscribe the movements. 



It is a form of the graphic method that M. Plateau 

 first adopted. He confined himself to perfect insects, and 

 directed his attention to (1) the form of the inspiration 

 and expiration ; (2) the parts of the body participating 

 in the respiratory movements ; (3) the expiratory and in- 

 spiratory muscles ; (4) the influence of certain parts of the 

 nervous system on the movements of respiration. The 

 technical processes concerning the muscles and nervous 



system are a matter of mere dissection, once the form of 

 respiratory movement is ascertained, and the latter, 

 therefore, chiefly claims notice in a simple resume. 



M. Plateau used two kinds of styles to inscribe the 

 movements on a rotating blackened cylinder. One was a 

 narrow light strip of Bristol paste-board, fastened to the 

 part of the body whose movement was to be ascertained, 

 with a little Canada balsam ; the other a lever of the third 

 order, turning freely about a horizontal axis placed at one 

 end, and resting by its own weight, at a point near the 

 axis, on the body of the insect (the insect, in either case, 

 being supported fixedly in any desired position). 



The graphic method is, however, unsatisfactory, and 

 sometimes quite inapplicable, and M. Plateau used 

 another along with it, viz. the method by projection, 

 which gave excellent results. 



The insect, fixed on a small support, so that the move- 

 ments in breathing are not interfered with, is introduced 

 into a large magic lantern lit with a good petroleum lamp. 

 A reversed silhouette is obtained on the screen, and if a 

 certain magnification be not exceeded (say 12 diameters), 

 a very distinct image is produced, on which one may 

 follow all the respiratory movements sufficiently amplified 

 to indicate real displacements of a fraction of a milli- 

 metre. With a sheet of white paper over the image one 

 draws the contours of the silhouette, corresponding to 

 expiration and inspiration. Further, by changing the 

 position of the insect, and by attaching short paper styles 

 at parts whose movements are doubtful, a complete know- 

 ledge may be acquired of all details of the respiratory 

 movements that characterise a given insect. 



With a little practice, not only may the respiratory 

 movements of small insects, such as flies, be easily 

 studied thus, but a number of questions are unmistak- 

 ably settled, which cannot be decided by direct observa- 

 tion. 



The following is a brief resume of the author's results : — 



1. There is no close relation between the form of the 

 respiratory movements of an insect, and the insect's 

 place in zoological classifications. The respiratory 

 movements are similar only when the structure of the 

 abdominal rings and the arrangement of muscles moving 

 them are nearly the same. Among curious facts here, 

 the movements of Phryganeidae are unlike those of nearly 

 related Neuroptera (such as Sialis), and like those of 

 sting-bearing Hymenoptera. 



2. In all insects the diameter of the abdomen diminishes 

 in expiration by approximation of the dorsal and sternal 

 arches of the segments ; in some cases the dorsal, in 

 others the sternal, showing the greater mobility ; and in 

 others both having nearly the same mobility. 



3. The modifications in the vertical diameter may be 

 accompanied by changes in the transversal diameter (e.g. 

 Libelluke). 



4. Contrary to a former view, the changes of length 

 of the abdomen, in normal respiration, by protrusion and 

 return of the rings, are rare in insects ; they are observed 

 in an entire group only in the case of the sting-bearing 

 Hymenoptera. Some isolated cases occur in the other 

 zoological subdivisions (e.g. the caddis flies among the 

 Neuroptera). 



5. In the majority of cases, the thoracic segments do 

 not participate in the respiratory movements of insects at 

 rest. But the respiratory displacements of the posterior 

 rings are less rare than Rathke supposed. 



6. It has been thought that the respiratory movements 

 in many insects were progressive, and propagated like a 

 wave either from the base of the abdomen towards the 

 point," or from the middle towards the two ends. This 

 wave is, however, an exceptional phenomenon, is absent 

 in all Coleoptera, in Acridians, in Libellulse, in sting- 

 bearing Hymenoptera, in Muscides, and a part of Lepi- 

 doptera, and only appears in isolated forms in certain 

 groups. 



