342 SPARKS FROM A GEOLOGIST^ HAMMER. 



animals and plants, long regarded distinct, are in truth 

 only transitional states of one of these species in its 

 passage over to the other. More properly, intermediate 

 states which have arisen simultaneously with the extreme 

 states. In many cases the varied states seem to sustain 

 relations to geographical position. Thus among plants, 

 peculiarities of situation have given us varieties of the 

 Juniper, Paper Birch, Chestnut Oak, Hackberry, Beach 

 Plum, Black Thorn, June Berry, Wild Rose, etc. Among 

 animals, extensive chorographical variations have been 

 noted among Echinoderns, by L. Agassiz, A. Agassiz and 

 E. Haeckel ; among Molluscs, by Cooper, Barber, Weatherby, 

 Lewis and others ; among insects, by Packard, Edwards 

 and Walsh ; among fishes, by Jordan, Putnam and L. 

 Agassiz ; among birds, by Baird, Allen, Ridgeway and 

 Coues; among mammals, by Baird, Allen, Coues and Yar- 

 row. In other cases the variations seem to be due to 

 marked changes in the physical environment of the ani- 

 mal. In a few cases it now appears that hybridity has 

 resulted in the establishment of intermediate and other- 

 wise variant forms.* 



Among fossil Brachiopods the variations and connect- 

 ing links are so numerous as to give rise to much per- 



* For hybrids among trees consult Gray, Man. Bot., N. U. 8. ; A. de Candolle, 

 Treatise on Oaks ; Naudin, Hybridity in the Vegetable Kingdom. But compare 

 Naudin, on the nature of heredity and variability in plants, in Comptes Rendus, 

 Sept. 27 and Oct. 4, 1875, and A. Gray, in Amer. Jour. ScL, III, xi, 153. On fer- 

 tile hybrids of common and Chinese geese, sec Youmans, in Quatrefages, Nat. 

 Hist, of Man, 143; C. Darwin, Nature, xxi, 207, Jaa 1, 1880; Kosmos, April 1880, 

 77. On fertile hybrids of the mallard and muscovy ducks, see T. M. Brewer, 

 Proc. Boston Soc. Nat. Hist., Jan. 21, 1874. On fertile hybrids of hare and rab- 

 bit, see Gindre, Bull, de la Soc. imp. Zodl. d' Acclimation, 1870, 659-67. On fertile 

 hybrids of goat and steinbock, see Von Tscluidi, Thierleben der Alpenwelt, 555; 

 C. Vogt, Kdhterq'aube u IVissenscJiaft, 66. On fertile hybrids of fox and dog, 

 see Von Tschudi, ib. 413; C. Vogt, id. 67. On fertile hybrids of wolf and dog, see 

 C. Vogt ib. 60, seq. 



