SKETCH OF PROFESSOR ALPHEUS HYATT. 263 



He obtained a much larger series of Planorbis than Hilgendorf had, and 

 was obliged to prove that, although there was a general gradation from 

 the flattened species to the spiral, through many intermediate forms, it 

 was not true that the series of species succeeded each other in time, as 

 claimed by Hilgendorf. All the species, in all their curious modifica- 

 tions, were found together in the lower stratum. Theoretically a 

 graded series was traceable ; and no doubt the flattened spiral forms 

 were the ancestors of the more conical spiral forms. He also pointed 

 out the marked resemblance between diseased and wounded indi- 

 viduals of a species, and the degraded form and the correlations of 

 these with the transformations taking place in the old age of other and 

 healthier species of the same group. He attributes his result to the 

 use of mechanical methods. The shells were gathered in bags, care- 

 fully labeled, from each stratum, taken home, sifted through graded 

 sieves constructed for the purpose, and every specimen, to the number 

 of several hundreds in each bag, was thus necessarily passed through 

 his hands. Professor Richard Owen, the eminent anatomist. Director 

 of the British Museum, has said of this memoir, " It is a model of the 

 mode in which such researches should be conducted." Besides these, 

 Professor Hyatt is the author of many smaller papers upon nearly all 

 subjects relating to natural history, and he has described many new 

 genera of cephalopods. 



Professor Hyatt has discovered that evolutionary changes in gen- 

 eral were much more rapid in earlier ages than now, and could be com- 

 pared closely with the isolated cases of very rapid evolution of forms 

 in such limited localities occurring in later times, as at Steinheim. For 

 instance, in the Silurian period there was a continual struggle for 

 better adaptation to the environment. In other Paleozoic ages, also, 

 evolution must have been rapid to have accounted for the observed 

 changes. It must have been particularly rapid immediately after the 

 groups or individuals originated, and thus should be represented as 

 expanding suddenly from their point of origin, like the spokes of an 

 expanded fan. He further believes that evolution of Cephalopoda has 

 taken place both by progression and retrogression, in four branches. 

 From the straight orthoceratic forms all fossil and modern Cephalopoda 

 have descended. To use his own words : " The efforts of the Ortho- 

 ceratite to adapt itself fully to the requirements of a mixed habitat 

 gave the world the Nautiloidea ; the efforts of the same type to become 

 completely a littoral crawler developed the Ammonoidea. The suc- 

 cessive forms of the Belemnoidea arose in the same way ; but here the 

 ground-swimming habitat and complete fitness, for that was the ob- 

 ject, whereas the Sepoidea represent the highest aims, as well as the 

 highest attainments, of the Orthoceratites, in their surface-swimming 

 and rapacious forms." No better group for the study of evolution is 

 found in fossil if erous beds, for in the shells every step of growth can 

 be traced, and it can be seen that the coiled forms all go through the 



