18 
MEMOIES OF THE NATIONAL ACADEMY OP SOIEXCES. 
group or superfauiily Tineina and allied forms, in some of which the mandibles still persist,^ and 
which in other features (besides having, as in Xepticnla and Phyllocnistis, nine jiairs of abdominal 
legs®) show their affinity to the Trichoptera and Mecoptera, originated at an earlier date. As is- 
well known, the Cretaceous land was covered with forests of oaks, lifiuidambars, maples, willows, 
sassafras, dogwood, hickory, beech, jioplar, walnut sycamore, laurel, myrtle, lig, etc., at or soon 
after the close of the Laramie epoch, and this may have been the time, if not earlier in the 
Mesozoic, when in all iirobability the low feeding caterpillars of that time began, perhaps through 
overcrowding, to desert their primitive herbaceous food ])Iauts and to ascend trees in order to feed 
on their leaves. 
Darwiif^ has made the significantremark that organic beings, when subjected during several 
generations to any change whatever in their conditions, tend to vary.” Farther on he refers to 
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. and he finally 
concludes: “Changes of any kind in the conditions of life, even extremely slight changes, often 
suffice to cause vai'iability. 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, blit also a slight climatic change, so to speak, involving a change in the temperature. Insects 
^Dr. A. W.altor has tUacovered the preseuce of miuute ruilimeutary mamliblea in the Eiiropeaa Micropierys: 
caltella, Tinea pclHonella, Tineola hmliellaj .irgyresthia nitidclla, Crambus instelluSf and two genera of PterophoridiB 
(Sitzmigsb. Jena, Oe^. fiir Med. ii. N’atiirwiss., 18^5). I have also detected them in Coleophora conidcipenHella and in 
another Tiueid of a genus as yet undetermined. 
2 The larvfB of Phyllocnistis have no thoracic legs, but have eight pairs of membranous retractile abdominal legs, 
and an anal pair. (American Entomologist, iii, 2511.) ^Ir. H. T. Stainton kindly informs me that the larvm of 
Nepticula have no thoracic legs “but possess nine pairs of abdominal logs,'’ which, however, bear no hooks; they 
look like so many deshy prominences." 
3 The Variation of Animals and Plants under Domestication, second edition, revised, London, 1888. In the 
same work Darwin says: ‘^Nathusins states positively (pp. 99, 103), as the result of common experience and of his 
experiments, that rich and abundant food, given during youth, tends by some direct action to make the head [of the 
pig] broader and shorter, and that poor food works a contrary result." 
Diirwin also states that ‘Hho nature of the food supplied during many generations has apparently affected the 
length of the intestines, for, according to Cuvier, their length to that of the body in the wild boar is as 9 to 1, iu 
the common domestic boar as 13.5 to 1, and in the Siam breed ils 16 to 1 " (Ib., 77). See also the cases mentioned by 
Semper iu his Animal Life, etc., pp. 60-62, and Xeauiayr’s St'imme dev Thierreichs, 1839, 123. Virchow claims that 
the characters of the skull depend on the shaxje of the jaw, this being due to dilFereuees iu food;*aiul here might be 
qupted the witty remarlrof Brillat-Savarin, Dis-moi ce quo tii manges, je te dirai ce qne tu es." 
The most remarkable case, and one directly ax)plicable to our subject of the probable cause of the growth of 
spines, is that cited by Prof. J. A. Kyder: “Even certain species of lishes, when well fed aud kept in conhnement, 
not only spawn several times during a season, instead of only once, as J am informed by Dr. W. H. Wahl, but also 
when kept from hibernating, 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 iu intensifying the 
monstrous variations of Japanese goldftshes, through selection, confinement in tanks and aquaria, with comparatively 
limited room for swimming, plenty of food, etc., all of which conditions tend to favor growth and metabolism, aud 
the expenditure of energy under such wholly new aud restricted conditions as to render it almost certain, as he 
thinks, that these factors have something to do with the devolopmout of the enormous aud abnormally lengthened 
pectoral, voutral, dorsal, double anal, aud caudal fins of his stock. Some of the races of these fishes have obviously 
been affected in appearance by abundant feeding, as is attested by their short, almost globular bodies, protuberant 
abdomens, aud greedy habits, as I have observed in watching examples of this short-bodied race living in Dr. 
Wahl’s aquaria. In these last instances we are brought face to face with modifications occurring iu fishes under 
domestication which are infinitely iu excess, morphologically speaking, of anything known among any other 
domesticated animals. That the abundant feeding and exposure to a uniform temperature daring the whole year 
and confinement iu comparatively restricted quarters have had something to do with the genesis of these variations, 
through an influeueo thus extended upon the metabolism alFocting the growth of certain parts of the body, which 
have tended to become hereditary, there can scarcely bo any doubt " (American Xaturalist, Jan., 1890). 
Darwin states that iu India several species of frosb-water fishes ‘^are only so far treated artificially that they 
are reared in great tanks; but this small change is sufficient to induce much variability " (Variatiou of Animals and 
Plant's under Domestication, ii, 246). 
