January 27, 1893.] 



SCIENCE. 



49 



as many young are produced as there would be if the nymph 

 were reared upon a vigorous young plant. I have seen mother 

 Aphlds, on old plants, which were not larger than nymphs after 

 their second moult on young plants. In the 13th generation this 

 point was well illustrated. Here we have the record of two 

 nymphs, the first, isolated Sept. 17 on an old pot-bound plant, did 

 not become a mother until Nov. 15, or 39 days after; while a 

 nymph, isolated 10 days later on a young, vigorous plant, attained 

 motherhood in 14 days. The 19th generation presents a similar 

 case. Nymphs born of these dwarfed and retarded mothers and 

 placed on young plants have become normal-sized mothers in 

 from 15 to 18 days in my cages. 



In one instance (54th generation) a nymph became a mother in 

 7 days, while one of the 14th gtneration was 35 days in attaining 

 the adult stage. I believe, that by carefully watching the Aphids 

 and always isolating the first nymphs bom upon young, vigorous 

 plants, that at least thirty generations of this Achyrantes Aphis 

 could be produced in a year. In 1890, Mr. W. J. MacNeil, while 

 studying a black chrysanthemum Aphis, at the Insectary, reared, 

 in 13 months and 5 days, thirty-two generations of the insect, all 

 agamic wingless females. As the table shows, I have reared 

 from twenty to twenty-five generations of the Achyrantes Aphis 

 in a year. 



As the experiment progressed, many other interesting facts were 

 learned which could not be included in the table. I will now 

 briefly discuss some of them. 



The mother Apbids were often caught in the act of giving birth 

 to a daughter. The operation required about five minutes, and 

 in every instance the nymph was born tail end first in a thin 

 transparent sheath or pellicle. Before being entirely delivered 

 from the mother, however, the nymph begins to work the pellicle 

 off; the antennae and first pair of legs are freed about the same 

 time, then follow the remaining legs and the honey-tubes, and 

 the pellicle appears as a minute whitish mass about the tail of the 

 nymph. The nymph remains attached to the mother until its 

 appendages are free and the little creature is able to stand alone. 

 There seems to he no published record of the young of wing- 

 less agamic female Aphids being born in a pellicle as just de- 

 scribed. Buckton gives five or six instances in as many genera 

 where the young of winged agamic females are born thus. I be- 

 lieve, however, that this manner of giving birth to their young is 

 as common among the wingless as among the winged agamic 

 forms of Aphids. I have observed it many times in the case of 

 Myzus achyrantes, and several times in the field among other 

 common species. Mr. MacNeil showed it to be true of the black 

 chrysanthemum Aphis; and Mr. W. E. Rumsey, while studying 

 the woolly apple-louse, Schizoneura lanigera, here at the Insectary, 

 watched underacompound microscope one of the wingless agamic 

 females giving birth to a daughter, and there was no doubt that 

 the nymph was born in a pellicle. This last case is contrary to 

 the observations of Mr. L. O. Howard as published in Comstock's 

 Report as U. S. Entomologist for 1879, p. 359; but the fact re- 

 mains that a wingless agamic female of Schizoneiira lanigera here 

 at the Insectary has been clearly seen in the act of giving birth 

 to several nymphs, each enveloped in a pellicle. 



The nymphs begin to suck the sap of the plant very soon after 

 birth, and as they increase in size moults occur. The minuteness 

 of the insects and the delicacy of their cast skins renders the ob- 

 servation of the Jiumbers of the moults very difficult. I woi'ked 

 nearly five months before I satisfactorily settled the fact that the 

 Achyrantes Aphis moults four times during its lifetime. My 

 method was to use a small plant with a few leaves and place a 

 piece of stiff black paper close around the plant on the surface of 

 the soil. This was necessary, as the delicate white cast skins 

 frequently fell from the plant and would have been easily lost 

 unless this smooth black surface had caught them. 



The records of four nymphs of the 7th, 9th, and 15th genera- 

 tions show that the first moult occurs from 3 to 4 days after 

 birth; the second from 3 to 5 days after the first; the third from 

 1 to 3 days after the second; and the fourth from 3 to 5 days after 

 the third. In one instance, when the growth of the nymph was 

 retarded by a stunted plant, its moults occurred about one week 

 apart. It requires from IS to 30 minutes to complete a moult. 



The nymphs of a black chrysanthemum Aphis and of Schizo- 

 neura lanigera also moulted four times, as recorded in the theses 

 of Messrs. McNeil and Rumsey. Pemphigus filaginis and Tetra- 

 neitra tttoj are also recorded as moulting four times; thus four 

 seems to be the normal number of moults among plant-lice. 



Under the more even temperature during all the seasons in a 

 green-house, plant-lice there do not show such a wonderful 

 fecundity and rapidity of production as has been recorded from 

 field observations. The table above shows that the seasons have 

 no material effect upon the rapidity with which the generations 

 are produced in a green house. 



To ascertain whether the fecundity of the Aphids diminished 

 through the successive generations of the agamic females, I 

 C'unted the number of nymphs born of a single mother in several 

 instances. During the 1st and 2d generations, 37 nymphs were 

 born of a single mother. In the 3d generation, 3 to 4 nymphs 

 were born each day of a single mother for 14 days in succession. 

 A mother of the 18th generation lived 63 days and gave birth to 

 59 joung. In the 30th generation a mother gave birth to 62 

 daughters in 19 days, or at the rate of three a day. Sixty-one 

 nymphs were born of a mother of the 35th generation in one 

 month. A mother of the 46th generation gave birth to 15 young 

 in 3 days. Fifty-four daughters were born to a single mother 

 of the 41st generation. And in the 54th generation a mother 

 gave birth to 55 young. It is thus seen that the reproductive 

 power of the agamic females has not decreased through nearly 60> 

 generations. 



Mr. MacNeil had one wingless agamic female of the black 

 chrysanthemum Aphis which gave birth to 70 young in 34 days; 

 at one time 7 were born in 37 hours. Mr. Rumsey reared in one 

 insiance 68 nymphs in 65 days from a wingless agamic female of 

 Schizoneura lanigera; this female lived 13 days after the birth of 

 the last nymph, and was nearly three months old when she died. 

 From another female Mr. Rumsey reared 86 young in 55 days. 

 Sereral of the agamic females of the Achyrantes Aphis have lived 

 two months after becoming mothers. 



To learn whether winged females might not be produced if the 

 plants became overcrowded with the Aphids, I allowed, in several 

 instances, reproduction to go on undisturbed in the cages. Sev- 

 eral hundred wingless females would accumulate on a small 

 plant, and possibly winged forms might have been forced in time 

 if in each instance the overcrowding had not been cheeked by a 

 fungous growth, which set in and destroyed a majority of the 

 insects. 



Many volumes have been written upoh the habits and life his- 

 histories of plant-lice; enough has been written upon the grape 

 Phylloxera alone to fill a small library. And yet we have much 

 to learn about plant-lice. I believe they present as varied, peculiar, 

 interesting, and wonderful phases in their habits and life his- 

 tories as do any other insects. 



THE EXTREME HEAT AND COLD ENDURED BY MAN. 



BY THE MARQUIS DE NADAILLAC, PARIS, PRANCE. 



The exceptional faculties of Man enable him, alone of all the 

 mammals, to battle with extreme cold as with extreme heat, and 

 it is with real astonishment that we ascertain what men of our 

 race can endure. In the earliest times of which we have any 

 knowledge, we have strong evidence that our species lived, both 

 in America and in Europe, when large extents of both continents- 

 were covered with ice and when his companions were the elephant 

 and the woolly rhinoceros. Later, the Aryan race, whatever 

 may have been its birthplace, reached step by step in the south 

 the Gangetic Peninsula, 8° only removed from the equator, and, 

 in the north, Iceland and Greenland, which seem the extreme 

 points attained by our most prolific race in those days so distant 

 from outs. 



A few years ago the English and Russian officials assembled at 

 Maruchak for the delimitation of Afghanistan suffered a mean 

 temperature of — 20° C, which was considered moderate in those 

 regions. In his eventful journeyacross the mountains of Central 

 Asia, utterly unknown to us, Prince Henry of Orleans had to 



