290 GENERALIZATIONS. 



several forms, that change which Prof. Heer has termed " the 

 remoulding of species." It may be admitted that several spe- 

 cies of our epoch were invested, in earlier periods, with forms 

 which bore a somewhat similar relation to the present form 

 which the larva bears to the fully developed animal. Indeed 

 many species of ancient periods may be compared to the larvae 

 or embryos * of those now living. 



Under another point of view the remoulding of species differs 

 materially from the alternation of generations (of the metamor- 

 phosis) ; for in that regenerative change all the individuals at 

 their last stage of development acquire the form belonging to 

 the mature insect, and only in the last form f attain to sexual 

 maturity. The whole series of forms in this metamorphosis 

 finally returns to the same point ; and consequently the species 

 always moves in the same circle, whilst the creation of new spe- 

 cies advances in a spiral to reach new points of development. 



Even when these new species owe their origin to species re- 

 sembling them, they will not resume the characters of the spe- 

 cies from which they proceeded, but for thousands and hundreds 

 of thousands of years they will preserve their determinate typical 

 characteristics which they obtained by their regeneration. To 

 Prof. Heer the origin of forms is a secret, an enigma, in the ex- 

 planation of which may be exercised the talents of divination, 

 but which has not been fully and entirely solved either in the 

 known phenomena of nature, or by the application of established 

 physical laws. 



* The featherstars (Comatulce) are mounted on stalks when young, and 

 resemble in that state the Encrinites of ancient epochs. Many fishes of those 

 early periods agree in some characteristics with the embryos of existing 

 fishes. Riitimeyer has recently shown that some Tertiary mammals exhibit 

 a great resemblance in their dental system to the arrangement of the milk- 

 teeth of several living species. 



t [Sir John Lubbock, F.R.S., mentions that recently Prof. Wagner (Zeit. 

 fiir Wiss. Zool. 1863) has discovered that "among certain small gnats the larvae 

 do not directly produce in all cases perfect insects, but give birth to other 

 larvae, which undergo metamorphoses of the usual character, and eventually 

 become gnats. His observations have been confirmed, as regards this main 

 fact, by other naturalists j and Grimm has met with a species of Chironomus 

 in which the pupse (or chrysalises) lay eggs (Mem. de 1'Acad. Imp. de St. 

 Petersbourg, vol. xv. 1870). * On the Origin and Metamorphoses of Insects/ 

 by Sir John Lubbock, p. 76. EDITOB.] 



