LA COLECCIÓN DEL MUSEO RAYO

8 : 22 Stripes StotKXKiry 18 12 Fig. 21.

Diagram summarising the responses obtained to d iffe re n t d irectio n s of s trip e movement.The figures represent the to ta l number of v is its to each secto r in each experiment

99.

Th# in s e c t to be te ste d was placed on the very sm all s tr ip o f wood (1 ” X 1” se ctio n ) and allowed to walk to the end. The strip ed cylin d er was then rotated eith er clockw ise or a n ti-clo ck w ise, T1» ine c ts were found to walk str a ig h t o ff the end of tiie s tic k (sin c e i t w s only 1” o ff the flo o r tiiis was accomplished very e a s ily by the 5th in sta r nymphs w ithout any disturbance of o rien ta ticjo ), Mote was taken o f tiie secto r in to which the in s e c ts walked.

In the Control runs tiio cylin d er was sta tio n a ry and a 4" square black o b ject was placed on the w all opposite to the 4” gap.

R esu lts, (F ig .21 ) The number o f animals tested was very sm all

(3 each ID tim es) but was s u f fic ie n t to show c le a r ly th a t the d ir e c tio n o f movement of the str ip e s had a marked influence on the d irectio n o f the anim als' track s. When the cylin d er was moving clockw ise so th e t the str ip e s moved across an anim al's ri^ h t eye from fro n t to rea r, the animal turned towards tiie gap (F ig . 21 )• ^hen the str ip e s moved from rear to fron t of tlie eye the in se c ts did not approach tim ^ep and tended to walk str a ig h t forward, curving s lig h t ly to tiie l e f t (F ig,2 1 )♦ In the con­ tr o ls the animals showed no s ig n ific a n t b ias ( ,3^ p ^ ,2) to e ith e r sid e (F ig . 21 ) .

'conclusions. The ejqperiraents tiius s-.ow th a t the horizon tal movement o f a sm all part o f the v isu a l f i e l d has a marked in flu en ce on the in se c ts * tracks and tliat tiie in s e c ts respond to movem%it over the eye both from fro n t to rear and from rear to fro n t. This la s t poin t was confirm d in la te r t e s ts on u n ila te r a lly blinded ani a ls in a rotating strip ed cylind er

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(r e s u lts not q u a n tita tiv e ). The importance o f th is w ill be discussed la te r .

Stim ulation o f d if f e en t parts o f the eye.

The previous experiment had shown the e f f e c t o f stin n ilation by iio r i- so n tal movement on the la t e r a l part of the compound ey e. The animals were now placed fa cin g the ^ap and te ste d as b efore. The cylind er speed was the same as in the previous t e s t .

R esu lts. (Table 3^ ) .

I t was found th a t in t h is situ a tio n the animals walked towards the gap q u ite accurately with l i t t l e d ev ia tio n to r ig h t or l e f t , although there was a s lig h t tendency to fo llo w the str ip e movement.

C onclusion. From the 2 a ove t e s t s i t can be concluded th at hori­ zon tal movement seen by t l» la te r a l part of the eye causes turning but when SAon by the fro n t o f the eyes has lo s s e f f e c t .

Importance of the Type o f Movement.

Auparatus. The animals were again placed facing the ap but tn ie time the r o ta tin g cy lin d er was com pletely white except for 2 black

str ip e s 4” broad d iam etrically op p osite. The ro ta tio n speed of the cylin d er was 1 rov. / 2 se c s, hence the stim u la tion e quailed 2 changes/sec. ( Interm ittent; long wtiite period sn ort black p erio d ), A con trol was performed with the cylin d er sta tio n a ry .

R esu lts. I t was found th t the in term itten t stim ulus supplied by the 2 moving str ip e s e lic it e d the fr ig h t response (Jerking with s lig h t

backing). The r e s u lts are presented in ta b le 3 6 lin e 3 and show th a t in the m ajority o f eases tlie fr ig h t response was observed and tlia t

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the in s e c ts rarely approaclied the , ap. In many cases tiiey s a t s t i l l or turned round on the s t ic k without showing aqy r sponse a t a l l to the movement.

C onclusion. Conparing the above r e su lts witli those obtained when the Cylinder is co jp letely covered w ith 1** black and w hite str ip e s

( previous expfrim ent) shows th at these 2 types of movemoct when seen by the same (fr o n t) part o f the ey^s e l i c i t d iffe r e n t resp o rses.

Ontopotor Responses - D iscussion.

The preceding experim ents have thus shown tn t the same movement (o f s tr ip e s ) produces d iffe r e n t responses when seen by d iffe r e n t parts of the eye. D iffer en t movements produce d iffe r e n t responses Wien seen the same part of the eye^ 1 hr the m ore the portion o f the v isu a l f ie ld occupied by the movement does not need to be large ( — 30®) and the

animals respond to mcvemonts o f shape over the eye both from fro n t to rear and from rear tv fro n t.

I t i s intfireetin^ to compare those r e su lts with what has been found for other in s e c ts . Thus lo c u sts fo llo w the d irectio n o f str ip e movement (when seen on the sid e of the eye) whereas some in s e c ts walk so as to oppose the str ip e m ovem ent.(e.g. bees,K echt and W olf,1929).

Again, whije the la te r a l portion o f the eye i s the one involved in the optomotor response in lo c u sts and many other in s e c ts , i t i s the an terior part of the eyes Wiich i s Important in Mantis (S ch liep er 192?) and in some cases the moving part of the v isu a l f ie ld has o ften to be larger ("Schlieper 192?) than fo r lo c u s ts . F in a lly , sane in s e c ts show l i t t l e or

1 D 2 .

no response to a movement over tlie eye from fron t to rear, e . g . , Aeschna nymphs (Tonner 1936) and the w eevil Calandra pranaria (L .) (Buddenbrock & H olier Hacke 1952), Since th»' r^'sponse in lo c u sts was not measured

q u a n tita tiv ely i t i s Im possible to sta te whetlier or not the in s e c ts r es­ pond eq u ally w e ll to movements fron t to r ar and rear to fr o n t, but i t i s n everth eless clea r th a t a response to movement from fron t to rear does e x is t in och lsto cerca .________

The fa c ts mentioned above, p a r ticu la r ly the response to movement over the eye from fro n t to r ar, are of groat sig n ific a n c e to the problem o f tlie d iffe r e n tia tio n o f su b ject and ob ject mcvement widch i s now to be d iscu ssed ,

Subject and Object Movetnmit.

The movement o f an image o f an o b ject over the r e tin a depends on the r e la tiv e motions o f ob ject aivi animal*, (fo r animals with unooveable e y e s ).

There arc a whole se r ie s o f con d ition s ranging from the s itu a tiw is where both o b ject and animal are moving to the extremes which a r e :-

1. O bject moving animal s t a t i nary

2. O bject sta tio n a ry animal moving.

As Buddenbrock s ta te s (1952) th ese situ a tio n s are fundam entally d iffe r e n t. I t i s th erefore necessary in any d iscu ssion on responses to movemont, to

* This does not include tlie phenomenon o f stroboscopic v is io n which is known to e x is t in in s e c ts ( e .g , see Autrum 1952^.

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