Natural History in Foreign Countries* 471 



quail discovered with one eye some poppy seeds, which are very small and 

 inconspicuous. (Se/miid, Bliken en den Haushaltder Natiir, p. 26. edit. 1826.) 



Of the Sight of krachiiidce^ Scorpion idee , and Stemmatous Insects. — The 

 smooth eyes of these animals are very analogous in their construction to 

 those of fishes ; only the anterior chamber of the eye is totally wanting, 

 and the iris is nothing more than a band of pigmentum bordering the ante- 

 rior surface of the glassy substance. The crystalline is not enchased in 

 the glassy substance ; the corresponding surfaces of these two bodies are 

 convex, and scarcely touch each other except in one point. The small 

 space which the crystalline leaves between it, the cornea, and the glassy 

 substance, is, probabl^^, filled up with a liquid in the living animal. In every 

 case refraction should be considerable in the stemmata, for it takes place, 

 1. by the convexity of the cornea; 2. by that of the crystalline, which 

 is denser than the cornea ; 5. by the posterior convexity of the crystal- 

 line to the passage of light in the space occupied, probably, by a liquid ; 

 4. and lastly, by the glassy substance. In consequence of this disposition, 

 the eyes, which are here treated of, must necessarily be purblind. Thus 

 spiders only see at very short distances. The position of these eyes, in a 

 great number of insects, and the fact that larvas have, in general, only stem- 

 mata, since they have nothing to see afar off, tends to confirm this opinion; 

 The field of sight in smooth eyes can be only very small : to this condition 

 their immobility and the diverging of their axis unite, to prevent, in spite of 

 their plurality, the different visual fields from covering themselves again, and 

 the double or multiple sight from taking place. 



In the ^Solpuga the large eyes diverge under an angle of 90°, the field of 

 vision cannot surpass that extent ; and in other Jrachnidae in which the 

 diverging is less, there is even some visual scope. The small pediculate eyes 

 of the jSolpuga are situated anteriorly upon the same plane, and their fields 

 of vision should cover themselves ; in other ^rachnidae, the eyes are always 

 placed upon an arc of the external integuments, sometimes united by pairs, 

 but always with diverging axes. The large eyes of the jSolpuga, and of other 

 scorpions, are probably less myopic than the small, less developed, and less 

 diverging stemmata of other Jrachnidae. {Miiller, zur Vergleichen Phys, 

 des Gesicht.) 



Rock Blocks. — M. Hausmann, whose profound knowledge of geology is 

 well known, has published an excellent memoir in Latin, under the title of 

 De Origine Saxorum per Germanice Septentrionalis Regiones arenosas disper- 

 soriim. He describes the dispersion and gradual wearing down of the in- 

 numerable erratic blocks found in the sandy plains of Northern Germany; 

 though, as M. Brongniart justly remarks, they are by no means confined to 

 this district, but extend east and west, as well as along the course of the 

 Danube. 



All their phenomena indicate a violent catastrophe which the northern 

 portion of the globe must have sustained at the period of its last general 

 change. M. Hausmann mentions the several theories devised to account 

 for these. Some geologists are of opinion that the blocks in question have 

 been formed in the localities which they now occupy, being the remains of 

 mountains which anciently occupied those plains. This opinion has been 

 defended by Beroldinger, and lately revived by Muncke ; but, though at 

 first sight it appears simple, it is disproved by the great diversity of the 

 species of rocks found indiscriminately together, though varying very far in 

 the dates of their formation. Some, for example, are enveloped in sand, in 

 clay, and in marl ; whilst others, entirely naked and isolated, rest upon a 

 posterior alluvion. The blocks, moreover, are «ot surrounded with stones 

 in such a manner as to support this opinion ; and their smooth surface, whe- 

 ther it be plain or rounded, proves that they must have long been exposed 

 to the influence of water. Other geologists suppose them to have been 



