February i6, 1893] NATURE 



375 



He thus succeeded in rotating a hollow cylinder of mica, or 

 other insulating substance, hung by a silk fibre, in the space 

 enclosed by four vertical curved copper plates, to which the 

 requisite differences of potential were communicated. An sCt- 

 count of these interesting experiments (described to the 

 Accademia dei Lincei) will be found in the Natunvissen- 

 fchafiliche Rundschau, No. 3, 1893. 



Prof. R. C. Schiedt has been making some interesting 

 observations on oysters, and at a recent meeting of the Phila- 

 delphia Academy of Natural Sciences Prof. Ryder reported on 

 his behalf that oysters which had the right valve removed and 

 were exposed to the light in this condition, in a living state for 

 a fortnight or so, developed pigment over the whole of the 

 epidermis of the exposed right mantle and on the upper exposed 

 sides of the gills, so that the whole animal from this cause 

 assumed a dark-brown colour. Animals so exposed not only 

 attempted to reproduce the lost valve and hinge, but also partly 

 succeeded in so doing, even re-establishing the insertion of the 

 diminutive pedal muscle upon the inner face of the imperfectly 

 reproduced right valve, which was deformed owing to the lack 

 of support of the right mantle, because of the removal of the 

 original right valve. As a consequence the right mantle was 

 rolled up at the edge, and this deformation of the mantle was 

 reflected in the attempted regeneration of the lost right valve. 

 The pigment developed during exposure to light in the mantle 

 and gills in oysters with the right valve removed, which were 

 kept alive in the aquaria at Sea Isle City by Prof. Schiedt, was 

 wholly confined to the epidermis as it normally is at the mantle 

 border in the unmutilated animal in nature. The inference to 

 be drawn from these facts is that the development of pigment in 

 the mantle and gills was wholly and directly due to the abnor- 

 mal and general 'stimulus of light over the exposed surface of 

 the mantle and gills, due to removal of the right valve, and that 

 the mantle border, the only pigmented portion of the animal, 

 is pigmented because it is the only portion of the animal which 

 is normally and constantly subjected to the stimulus of light. 



Mr. D. CLEVELAND,of San Diego, California, contributes to 

 Science an article in which he states some curious facts regarding 

 the trap-door spider {Mygale henzii, Girard), which is widely 

 diffused in California. Behind San Diego there are many hil- 

 locks about a foot in height and three or four feet in diameter. 

 These hillocks are selected by the spiders, Mr. Cleveland sug- 

 gests, because they afford excellent drainage and cannot be 

 washed away by the winter rains. A suitable spot, which 

 always consists of clay, adobe or stiff soil, having been chosen, 

 the spider excavates a shaft varying from five to twelve inches in 

 depth, and from one-half to one and a half inches in diameter. 

 This is done by means of the sharp horns at the end of the 

 spider's mandibles, which are its pick and ^shovel and mining 

 tools. The earth is held between the mandibles and carried to 

 the surface. When the shaft is of the required size, the spider 

 smooths and glazes the wall with a fluid which is secreted by 

 itself. Then the whole shaft is covered with a silken paper 

 lining, spun from the animal's spinnarets. The door at the top 

 of the shaft is made of several alternate layers of silk and 

 earth, and is supplied with an elastic and ingenious hinge, and 

 fits closely in a groove around the rim of the tube. This door 

 simulates the surface on which it lies, and is distinguishable 

 from it only by a careful scrutiny. The spider even glues earth 

 and bits of small plants on the upper side of the trap-door, thus 

 making it closely resemble the surrounding surface. The spider 

 generally stations itself at the bottom of the tube. When, by 

 tapping on the door, or by other means, a gentle vibration is 

 caused, the spider runs to the top of its nest, raises the lid, and 

 looks out and reconnoitres. If a small creature is seen, it is 

 seized and devoured. If the invader is more formidable, the 

 NO. 12X6, VOL. 47] 



door is quickly closed, seized, and held down by the spider, so 

 that much force is required to open it. Then the spider drops 

 to the bottom of the shaft. When the door of the nest is 

 removed, the spider can renew it five times — never more than 

 that. From forty to fifty cream-coloured spiderlings are hatched 

 from the yellow eggs at the bottom of the nest. When these 

 have attained only a fraction of their full size — before they are 

 half grown— the mother drives them out into the world to shift for 

 themselves. After a brief period of uncertainty they begin active 

 life by making nests, each for itself, generally close to " the old 

 homestead," sometimes within a few inches of it. These nests are 

 always shallow and slender, and are soon outgrown. When the 

 spider attains its full size it constructs a larger nest. 



An interesting paper concerning the supposed volatility of the 

 element manganese is contributed by Prof. Lorenz and Dr. 

 Heusler, of Gottingen, to the current number of the Zeitschrift 

 fur Anorganische Chemie. Although the melting point of the 

 metal is known with tolerable certainty to be about 1800° — 

 1900", much higher than that of iron, no information has yet 

 been acquired concerning its boiling point. Profs. Lockyer 

 and Chandler Roberts, however, so long ago as 1875 pointed 

 out that the metal was volatile at the temperature of the oxy- 

 hydrogen blowpipe ; and M. Jordan, in a communication to the 

 Coinptes Rendus in the year 1878, reported that in the manu- 

 facture of highly manganiferous spiegeleisen near Marseilles, a 

 deposit very rich in manganese was usually found in the cooler 

 portions of the furnace. Moreover, M. Jordan stated that during 

 the casting of ferro-manganese red flames are produced, from 

 which a heavy fume is deposited containing a large percentage 

 of manganese. M. Jordan subsequently heated ferro-manganese 

 to a white heat in a crucible in his laboratory, and ascertained 

 that a diminution in the percentage of manganese actually 

 occurred. These observations were considered somewhat sur- 

 prising, inasmuch as the melting point of manganese is so high, 

 in the neighbourhood of white heat, and it would appear that 

 this volatility must be exhibited even at the melting point itself. 



Prof. Lorenz and his colleague have therefore conducted a 

 series of experiments with the view of ascertaining whether 

 manganese is really volatile per se, or whether the volatility is 

 due to the intermediate action of carbon monoxide (derived 

 from the carbon usually present) in forming a volatile but dis- 

 sociable compound of a nature similar to nickel- and iron- 

 carbonyl. It was first definitely proved that carbon monoxide 

 does not combine with manganese below the temperature of 

 350°, a fact which M. Guntz has recently independently pointed 

 out. Experiments were then made at higher temperatures, 

 using a new form of combustion furnace, designed by Prof. 

 Lorenz and fully described in the Zeit^^chrift, in which each 

 individual burner is supplied with a blast capable of being 

 regulated, the whole apparatus being equivalent to a row of 

 blowpipes which will rapidly raise a thick porcelain tube up 

 to a white heat. In the first series of these high temperature 

 experiments coarsely powdered manganese containing seven per 

 cent, of carbon was heated to whiteness in a glazed porcelain 

 tube in a current of carbon dioxide, in order that nascent carbon 

 monoxide might be produced in contact with, manganese by the 

 reduction of the carbon dioxide by the carbon present. After 

 half-an-hour's heating the tube was allowed to cool in the stream 

 of carbon dioxide and then broken, when it was found that a 

 large quantity of the manganese had volatilised and condensed 

 again further along the tube, in the form of a thick black deposit 

 somewhat resembling zinc dust. Upon repeating the experiment 

 with a current of carbon monoxide, a similar result was ob- 

 tained. Hence manganese is certainly volatile in carbon 

 monoxide. But it was afterwards found that equally good 

 deposits of manganese dust were obtained when a current of 



