2/4 



NA TUBE 



lJulv iS, 1907 



wilehs, Belia'is, and Ismailis, were also encountered 

 by the way. 



In northern Syria two of the most interesting 

 places visited by Miss Bell are the castle of Kala'at 

 el-Husn, near Horns, and the church of Kala'at 

 Sirn'an, between Aleppo and the Bailan Pass. 

 Kala'at el-I4usn is the northern Kerak, the " Crac 

 des Chevaliers " of Crusading times, and is one of 

 the finest examples of the military architecture of the 

 Crusaders in existence. Fig. i, a photograph by 

 Miss Bell, gives an idea of the walls with their 

 French round towers and Saracenic sloping walls. 

 The castle belonged to the Hospitallers, and the 

 Grand Master of the Order lived there, until it was 

 taken by the Egyptian Sultan Malek edh-Dhaher. 

 This, then, was the first stronghold of the Order of 

 St. John, to be succeeded by Rhodes, always asso- 

 ciated with the name of de I'lsle Adam, and by 

 Malta, the scene of the heroism of la Valette and the 

 cowardice of Hompesch. 



Kala'at Sirn'an (Fig. 2), the scene of the fakir- 

 life of St. Simon Stylites on his pillar, is a fine 

 example of a Byzantine church of the sixth century. 

 Kalb Lozeh (p. 302) is just such another. Many of 

 these splendid specimens of Syrian stone architecture 

 have been studied by the recent archasological expedi- 

 tion of Princeton University. 



At beautiful Antioch and Seleucia Miss Bell's 

 Syrian journey ended. 



It is a pity that her map is not better than it is. 

 It is based on Kiepert's map in Oppenheim's " Vom 

 Mittelmeer zum Persischen Golf," with additions and 

 Miss Bell's route marked in red. All the German 

 spellings of Arabic names seem to be retained un- 

 altered, with the result that the British reader is con- 

 fronted with such words as "Mcschetta," "'Ijun," 

 *' il-Kreje," " Riat," " Dimaschk Ischscham," and so 

 on, which he will hardly recognise as the " Mshitta," 

 "Ayun," " el-Kreyeh," " Ghiath," and Damascus 

 " Esh-Sham " of Miss Bell's text. This is a bad 

 fault, but one often committed when German maps 

 are copied in England. By the average British reader 

 " Ijun " and " Kreje " will be oronounced " Eve- 

 jiin" (Germ. "Eidschan ") and " Kreege " (Germ. 

 " Kridsch "). It is too often forgotten that the 

 German pronunciation of consonants and vowels is 

 not yet the world-standard, and that the English 

 pronounce the letters "j," " sch," "ch," quite" dif- 

 ferently from the Germans. We certainly will not 

 have the German " j " thrust down our throats, at 

 any rate. Miss Bell and her publishers must share 

 the blame for this serious blot on her otherwise admir- 

 able book. H. R. Hall. 



HAVE ALL EYES THE POWER OF 

 FORMING IMAGES?^ 



SOME animals, such as the earthworm, have no 

 eyes, and yet they are phototropic either in a 

 positive or negative sense, according as they move 

 towards or away from light. Others, such as 

 planarians, have remarkably simple eyes, consisting 

 of one or several sense elements, behind which is a 

 pigmented cup, composed of one or more cells. 

 Such eyes cannot form an image, and they have been 

 called " direction eyes " because light from only one 

 direction can affect such an eye at a given time. 

 Higher in the scale we find the " compound " or 

 " mosaic " eye, as in insects and other animals. The 

 question arises, To what extent is an image or 

 images formed by such an eye composed of many 



' "An Kxperimenl.ll StuHy nf ihe Im.^q'-'o mine Pom ersr.r Vaiinu>: Tvpes 

 of Ejes." Hy Leon \. Cole. Zo^IosiiafLal oratorv of irieMu eiin. of Com- 

 parative Zoology at Harvard ColleEe. (Pr r. of Ame.ican .Acdemy of Arts 

 and Sciences, vol. xlii.. No. 16, January, 1507.) 



ocelli? There can be no doubt that the compound 

 eye forms an image or images. Exner has taken a 

 photograph through the eye of a fire-liy, and Parker 

 has shown that the compound eyes of Astacus form 

 a single image. Lastly, we find in vertebrates the 

 " simple " eye, the optical construction of which leads 

 to the formation of an image on the retina. The 

 image of a distant object can readily be seen on the 

 retina of a fresh eye removed after death from an 

 albino rabbit, and if a lighted candle be placed in 

 front of the isolated eye of a frog, a beautiful little 

 inverted image of the flame may be visible on the 

 sclerotic. 



Mr. Leon Cole recently investigated the question 

 as to the formation of images by different kinds 

 of eyes by a new and ingenious method. It is obvious 

 that it would be almost impossible to make a direct 

 observation on the formation of an image bv certain 

 kinds of eyes, especially mosaic eves of very small 

 size. Mr. Cole's " aim has been, rather, to treat the 

 formation of images from the point of view of their 

 relation to the animal as a living organism — to 

 determine in what way the ability to form a more or 

 less perfect image affects the responses of the animal 

 to light, and what relation, if any, this result has to 

 the normal habits of the creature, and to its behaviour 

 under experimental conditions " (p. 337). 



For phototropic observations, Mr. Cole devised an 

 arrangement by which two sources of illumination 

 were so placed as to cau,se one or other to illuminate 

 the eyes. The animal was placed with its long axis 

 at right angles to a line joining the two lights. One 

 light was so much larger than the other that the ratio 

 of the two areas illuminated was as 10,000 to i. 

 The intensity of the light from either source was 

 about 1.25 candle metres. The qualities of the two 

 lights were also compared and tested, and the differ- 

 ences in the spectral components were so slight as 

 to be negligible. The experimenter wished to ascer- 

 tain " to what extent complexity in the organisation 

 of eyes is correlated with the reactions to luminous 

 areas of different size but of equal total luminosity " 

 (p. 347). The character and relative percentage of 

 phototropic responses as movements to or from lights 

 were used as measures of the reactions. Suppose an 

 animal positive in its reactions to directive light is so 

 placed as to be midway between two luminous areas 

 of the same shape, size, and intensity, the one acting 

 on the right eye and the other on the left. Assume that 

 each luminous area is i cm. square, has an intensity 

 of 100 candle-power, and is 2 metres from the animal. 

 The measure of the licrht falling on each eye would 

 be 25 candle mi'tres. Thus simultancouslv stimulated 

 on each side, the animal might go straight ahead 

 without turning, or it might turn at random towards 

 one light more than the other, and as the animal 

 is positively phototropic it would continue to crawl 

 towards this light. But as the chance of random 

 movements in one direction is as great as in the 

 other, in a large number of trials, we should find the 

 number of times that the animal would go towards 

 each light would be practically equal. Enlarge one 

 of the areas to 100 cm. square, but keep the total 

 amount of lieht the same. The area being 10,000 

 times as great, the intensity from i sq. cm. is now 

 only o-oi candle-power. The whole amount of light 

 on each side is still the same, 25 candle metres. 

 If the animal had no light-perceiving organs, the 

 reactions would be the same as when the lights 

 were of e(]ual size; the animal would be indifferent. 

 But if it had cells sensory to light distributed in its 

 skin, as there is no apparatus for concentrating the 

 light, the amount of lip-ht received at any point of 

 the skin on either side of the animal would be equal to 

 that received by any other. " This is evident from 



NO. 1968, VOL. 76] 



