18 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



f;roup or siipcrfainily Tiiieina and allied forms, in some of which the nuuidibles still persist,' and 

 which in other features (besides having, as in Nepticula and Phylloenistis, nine jjiiirs of abdominal 

 legs^) show their affinity to the Trichoptera and Mecoptera, originated at an earlier date. As is 

 well known, the Cietaeeons land was covered with forests of oaks, licinidanibars, maples, willows, 

 sassafras, dogwood, hickory, beech, poplar, walnut sycamore, laurel, myrtle, lig, etc., at or soon 

 after the close of the Laranue epoch, and this may have been the time, if not earlier in the 

 ]\Ieso/.oic, when in all probability the low feeding cater|)illars of that time began, perliai)s through 

 overcrowding, to desert their pi'iniitive herbaceous food plants and to ascend trees in order to I'eeCL 

 on their leaves. 



Darwin ' has made the significant remark " th;it organic beings, when subjected during several 

 generations to any change whatever in their ('onditions, tend to vary." Further on he refers ta 

 the general arguments, which appear to him to have great weight, " in favor of the view that 

 variations of all kinds and degrees are directly or indirectly caused by the conditions of life to 

 which each being, and more especially its ancestors, have been exposed'' (p. -41), and he linally 

 concludes: "Changes of any kind in the conditions of life, even extremely slight changes, often 

 suffice to cause variability. Excess of nutriment is perhaps the most efficient single exciting 

 cause" (p. 258). 



When, in Mesozoic or possibly still earlier times, caterpillars began to migrate from herbaceous 

 plants to trees, they experienced not only some change, however slight, in the nature of their 

 food, but also a slight climatic change, so to speak, involving a change in the temperature. Insects 



'Dr. A. Walter has discovered the preseuce of miaute rudimeutary mandibles iu the Europeaa Micropteryx 



calteUii, Tinea piilinnella, Tiiieola bisetiella, Argi/reslMa uilidMa, Crambiis trinlMm, and two genera of Pteroplioridiii 

 (.Sitzungsl). Jena, Ges. flir Mod. u. Natnrwi.ss., 18:55). I have also defeotoil thcin iu Coleaphara contscipeniwlhi and iu 

 another Tiueid of a genus as yet undetermined. 



'The larval of Phylloiui.stis have no thoracic legs, but have eight pairs of membranous retractile abdominal legs, 

 and an anal pair. (Amerieau Entomologist, iii, 2.")6. ) Mr. H. T. .Stainton kiniUy iuforms me that the larvie of 

 Neptiijula have uo thoraeic legs "but possess nine pairs of abdominal legs," whicli, however, bear no hooks; " they 

 look like so many fleshy promiucnees." 



^The Variation of Animals aud Plants uuder Domestication, second editiou, revised, Loudon, 1SS8. Iu the 

 same work Darwin eays : "Nathusius states positively (pp. 99, 103), as the result of common experience and of his 

 experiments, that rich aud abundant food, given during youth, tends by some direct action to make the head [of the- 

 pig] broader aud shorter, and tluat poor food works a contrary result." 



Darwin also states that '• the nature of the food supplied duriiig many generations has apparently affected the 

 length of the intestines, for, according to Cuvier, their length to that of the body in the wild l)oar is as 9 to 1, iu 

 the comuiou domestic boar as 13.5 to I, and in the Siam breed as 16 to 1 " (lb., 77). See atso the cases mentioned by 

 Semper in his Animal Life, etc., pp. 60-62, aud Neumayr's St.'lmme der Thierreichs, 1889, 123. Virchow claims that 

 tlie characteis of the skull depend on the shape of tlie Jaw, this being due to differences in food; aud here might be 

 i|Uoted the witty remark of lirillat-Savarin, " Dis-min co quo tu uiauges, je te dirai ce que tu es." 



The most remarkable case, aud one directly applical)le to our subject of the proliable cause of the growth of 

 spines, is that cited by Prof J. A. Ryder: " Even certain species of tishes, when well fed aud kept in conliueuieut,. 

 not only spawn several times during a season, iuste:id of only once, as I am informed by Dr. W. II. Wahl, but also 

 when kept from hibcruatiug, as he suggests, tend to vary in the most astounding manner. The wonderful results of 

 Dr. Wahl, attained iu the comparatively short period of six years, show what may be done in intensifying the 

 monstrous variations of Japanese goldftshes, through selection, confinement in tanks and aquaria, with comparatively 

 liuutod room for swimming, plenty of food, etc., all of which conditions tend to favor growth and metabolism, and 

 the expenditure of energy under such wholly new and restricted couditiona as to render it almost certain, as he 

 thinks, that these factors have something to do with the development of the enormous and abnormally lengthened 

 [leetoral, ventral, dorsal, double anal, and caudal fins of his stock. Some of the races of the.se fishes have obviously 

 been affected iu appearance by abundant feeding, as is attested by their short, almost globular bodies, protuberant 

 abilomens, aud greedy habits, as I have observed iu watching examples of this short-bodied race living in Dr. 

 Wahl's aifuaria. In these last instances wo are brought face to face with modifications occurring iu fishes under 

 domestication which are infinitely in excess, mori)h(>logically speaking, of anything known among ;iny other 

 domesticated auiuuils. That the abundant feeding and exposure to a uniform temperature during the whole year 

 and confiiu'ment in comparatively restricted quarters h.avo had something to do with the genesis of these variations, 

 through an iuUucuce thus extended upon the metabolism affec'ting the growth of certain parts of the body, which 

 have tended to become hereditary, there can scarcely be any doubt" (Ainerican Naturalist, Jan., 1890). 



Darwin states that in India several species of fresh-water fishes "are only so far treated artificially that tliey 

 are reared iu great tanks; but this small change is sufficient to induce much variability " (Variation of Animals and 

 Plants under Domestication, ii, 246). 



