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possibility. With the habitual positions of 

 our eyes, the axes are neither parallel nor 

 too convergent, and we see dimly two im- 

 ages of our nose and objects too near our 

 eyes. Now, when corresponding parts of 

 two stereoscopic pictures are apart from 

 one another only one inch and a half or so, 

 and are distant from our eyes one foot or 

 so, to combine the two pictures our eyes 

 are only required to take one of their ttabit- 

 ual positions ; that is, the axes of the eyes 

 need only to be so placed as if we were look- 

 ing at an object distant from our eyes two 

 feet or so : hence the effort required is very 

 trifling, even when unaided by any instru- 

 ment. But when the two pictures are so 

 separated by a partition that the right eye 

 can see only the right picture and the left 

 eye the left picture, the combination of the 

 two will take place as easily as with an or- 

 dinary stereoscope. This is, I think, chiefly 

 owing to the fact that as long as the two 

 pictures are seen separate^ the picture seen by 

 each eye is covered by a dim irnaje of the 

 partition seen by the other eye, and it is only 

 when they combine that we have a clear and 

 distinct view of the pictures. — M. Totama. 



Natural Selection. — An interesting case 

 of the operation of the law of natural selec- 

 tion and the survival of the fittest is re- 

 counted in the American Naturalist, by S. 

 F. Clarke. Having obtained a number of the 

 gelatinous egg-masses of one of our native 

 salamanders, he placed them in large glass 

 jars, where they developed rapidly. After 

 their gills and balancers had developed, they 

 emerged from the eggs and began their ac- 

 tive life in the water. A difficulty now ap- 

 peared — the author could not discover the 

 proper kind of food. Upon watching the 

 animals closely, however, he soon found 

 that they were eating off" one another's gills. 

 Closer examination showed that among the 

 many were a few individuals which, although 

 they came from the same parents and were 

 subjected to the same conditions while in 

 the egg, were yet gifted with greater vigor 

 than most of their fellows. These few 

 stronger ones ate off the gills of many of the 

 weaker, and at the same time were enabled 

 to protect their own gills from mutilation. 

 These favorable conditions, the large supply 

 of food, and the better aeration of the blood, 



soon began to show their influence upon the 

 growth of the favored individuals. Within a 

 week or ten days from the time of emergence 

 from the egg, these favored few were fifty per 

 cent, larger than their weaker comrades who 

 were born upon the same day. Their mouths 

 had by this time so increased in size that, 

 no longer satisfied with nibbling off the gills 

 of their brethren, they now began to swal- 

 low them bodily. Soon they were ten or 

 twelve times as great in length and bulk as 

 their victims. 



Carnivorous Caterpillars. — A striking 

 peculiarity of the caterpillars of Patago- 

 nian Lepidoptera, namely, their cannibalism, 

 is noticed by Prof. Carl Berg. All cater- 

 pillars in Patagonia, of whatever family 

 or group, prey upon their own kind. He 

 kept them in captivity, and found that, even 

 with an abundance of food-plants at hand, 

 they preferred to devour one another, " hair 

 and hide ; " they even tear open the cocoons 

 and prey on the chrysalids. One was ob- 

 served to devour in twenty-four hours six 

 or seven individuals of its own species. 

 This peculiarity of Patagonian caterpillars 

 is thus explained by the author: During 

 the summer there are extreme heat and 

 drought in Patagonia, and these causes, 

 together with the prevailing dry winds, 

 parch the vegetation, scanty at best. The cat- 

 erpillars are in consequence greatly strait- 

 ened for food, and the struggle for life has 

 led them to seek some other means of sub- 

 sistence. Hence their cannibalism, which, 

 being transmitted by heredity from genera- 

 tion to generation, becomes a second nature, 

 and the practices to which they were at 

 first driven by want they now perpetuate 

 through habit. 



A Battle-Royal among Ants. — F. E. Co- 



lenso, of Maritzburg, Natal, in a letter to 

 Nature, gives an animated description of a 

 fierce battle between ants, which he found 

 engaged in mortal combat on his garden- 

 wall. Among the ants was a considerable 

 number of larger individuals, " the soldier- 

 ants " of the same species, and the whole 

 ant community seemed to be bent on de- 

 stroying them. A group of little ones 

 would fasten on to a big one, the latter in 

 the mean time making desperate efforts to 



