18 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



frroupor superfamily Tiiieina anil allied forms, in some of which the iiuuuliblcs still persist/ and 

 which in other features (besides having, as in Nepticula and Phyllocnistis, nine i)airs of abdominal 

 legs') show theirattinity to the Trichoptera and Mecojjtera, originated at an earlier date. As is 

 well known, the Cretaceous land was covered witii forests of oaks, lii|aiilanibars, maples, willows, 

 sassafras, dogwood, hickory, beech, poplar, walnut sycamore, laurel, myrtle, tig, 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 probability the low feeding caterpillai's of tliat time began, perhaps through 

 overcrowding, to desert their pinmitive herbaceous food plants and to ascend trees in order to feed 

 on tlieir leaves. 



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

 generations to any change whatever in their conditions, tend to vary." Further on he refers to 

 the general arguments, wliich 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 esi)ecially its ancestors, have been exposed"' (p. l.'41), and he finally 

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

 suffice to cause variability. Excess of nutriment is perha])s the most efficient single exciting 

 cause" (p. 25S). 



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 presence of minute nidimeutary raimdibles iu the European Micropter/ix 

 cdllelhi, Tinea pvUionella, Tiiieola biseliella, Jrgiiri'slliia iiitiililla, Cramhnu trinlelliit, and two geuera of I'terophoridie 

 (.Sitzungsl). Jena, (Jes. fiir Med. u. Natnrsviss., IS:).')). I have al.so detected thoin in Coleophora voritscipeiiiu-Ua and iu 

 another Tineid of a genus as yet uudetermiued. 



'The larviB of Phyllocnistis have no thoracic legs, but have eight ])airs of membranous retractile abdominal legs 

 and an anal pair. (American Entomologist, iii, 25(5.) Mr. H. T. Stainton kindly informs mo that the larvie of 

 Xepticula have no thoracic legs "but possess nine pairs of abdominal legs," which, however, bear no hooks; " they 

 look like so many fleshy prominences." 



'The Variation of Animals and Plants under Domestication, second edition, revised, London, 1888. In the 

 same work Darwin gays : "Nathiisius 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." 



Darwin .also states that '•the n.aturo of the food supplied during many generations has app;irenlly affected the 

 Iciigth of the intestines, for, according to Cuvier, their length to that of the body in the wild boar is as 9 to 1, in 

 tlie cnmmou domestic boar as 13.5 to 1, and in the .Si;im breed as 16 to 1 " (lb., 77). See also the cases mentioned by 

 .Semper in his Animal Life, etc., pp. C>0-(52, and N(Mimayr's .St'imine der Thierreichs, 1889, 123. Virchow claims that 

 the characters of the skull depend on the shape of the Jaw, this being due to dilfereuces in food; an<l here might be 

 i[iioted the witty remark of Brillat-S.avarin, "Dis-moi ce <|ue tu manges, je te dirai ce ipie tu es." 



The most remarkable case, and one <lirectly aiiplical>le to our subject of the probal)le cause of the growth of 

 spines, is that cited by Prof. J. A. Ryder: "Even certain species of fishes, when well fed and kept in conhuement, 

 not only spawn several times during a season, instead of only once, as I am informed by Dr. W. H. Wahl, but also 

 when kept from hibernating, as ho 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 bo done in intensifying the 

 monstrous variations of J.apauese goldfishes, tliroughs(dcction, confinement in tanks and aquaria, with comparatively 

 limited room for swimming, plenty of food, etc., all of which conditions tend to favor growth an<l metabolism, aud 

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

 thinks, that these factors have something to do with tlio development of the enornu)Us and abnormally lengthened 

 ])e(^toral, ventral, dorsal, double anal, aud caudal lius of his stock. Some of the races of these Ushes have obviously 

 been affected in appearance by abnn<lant feeding, as is attested by their short, almost globular liodies, protuberant 

 abdomens, and 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 in fishes under 

 domestication which are infinitely in excess, morphologically speaking, of anything known .among any other 

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

 and confinement in comparatively restricted quarters have had something to do with the genesis of those variations, 

 through an influence thus extended upon the metabolism atlecting 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 in India several species of fresh- water fishes "are only so far treated artificially that they 

 are rean^l in great tanks; but this small change is sufficient to induce much variability" (Variation of Animals aud 

 Plants under Domestication, ii, 21Gj. 



