28 SCIENTIFIC ILLUSTRATIONS [Ble 



signal for its destruction. The shell closes not only at the side 

 but top, the latter action being effected by the separation of 

 the pointed ends, and the captive is either crushed to death, 

 or soon perishes from confinement. Here is a lesson to men 

 who are audaciously aggressive in their cupidity. The pinna 

 which you covet may encompass you ! o. s. 



Blessings in Unexpected Places. 



Poor as may be the fauna of the desert, there is yet cause 

 enough for astonishment that the species which compose it, 

 especially the herbivora, should be able to find subsistence in 

 these seas of sands, where they can find but a few saline plants 

 scattered at rare intervals, and where fresh water is almost 

 wholly wanting. It is, however, well known nowadays that 

 the wilderness provides its denizens with an aliment, which is 

 sometimes very abundant, suitable for man, the camel, and the 

 beasts, and is considered identical by many authorities with the 

 manna of the Bible. This substance is a cryptogamous vege- 

 table, variously christened lichen esculentus (Acharius), lecanora 

 esculenta (Pallas), luttarut (by the Arabs), and vassela-el-ard, 

 (by the Algerines). It sometimes forms on the sand, in the 

 morning, a layer one or two inches in thickness, and appears 

 to have dropped from heaven, or to have sprung spontaneously 

 from the soil during the night. It is probable that its spores, 

 transported by the wind, are developed by the humidity which 

 is condensed through the nocturnal coldness. A growth like 

 this teaches us not to be depressed on occasions when we may 

 happen to be in the wilderness tracts of our life. For we often 

 find blessings in unexpected places. Do not be afraid of the 

 wilderness when you remember the manna, and observe in this 

 wonderful provision of Nature how much of aptness there is in 

 Isaiah's allusion to the wilderness as a fruitful field. D. 



Blessings are Relative. 



In the recesses of the great cave of Kentucky, miles under 

 ground, there are waters which no ray of sunlight ever reaches, 

 and which are inhabited by blind insects and blind fishes. Dr. 



