The Life and Writings of Agassiz. 11 



and the Lepiddidians, which were inoffensive, and probably 

 omnivorous fishes, somewhat resembling the Carp in appear- 

 ance, but having no representatives in the present creation. 

 These researches attiong the fossils had not a geological 

 interest alone. The numerous examinations that M. Agassiz 

 was obliged to make, in order to establish, in all points, 

 the analogy of extinct species with living types, revealed to 

 him anatomical relations of great interest, which had been 

 hitherto passed over. He thus discovered the important fact, 

 not before made known, that there exists a remarkable pa- 

 rallelism between tlie development of the individual, and the 

 development of the whole class in the series of ages. In the 

 early stages of embryonic life the vertebral column does not 

 exist. In place of it there is found, in the embryo, a gela- 

 tinous mass, called the dorsal cord. Around this cord (which 

 remains for a longer or shorter time in all fishes) are formed 

 the vertebrga, as bony rings. These rings gradually increase, 

 and encroach more and more upon the dorsal cord, which, in 

 most fishes, at last disappears. In some types, however, — for 

 example, in the Sturgeon, — it remains during the whole life, so 

 that this fish has no vertebrae, and the apophyses rest imme- 

 diately on the dorsal cord. Now, Agassiz shows us that this 

 is the case with all the fishes of former epochs. They all 

 have distinct spinous apophyses, often very strong and com- 

 pletely ossified, but they show no trace of separate verte- 

 brae ; whence he concludes that these organs were wanting, 

 and that the dorsal cord continued throughout life, as in the 

 Sturgeon. As to the relative superiority of living types, also, 

 embryology reveals to us a wonderful parallelism. There is 

 no fish, however imperfect, whose organization does not cor- 

 respond to some place in the life of more perfect types. Take, 

 for example, the lamprey, or that still more imperfect fish 

 known under the name of Amphioxus, or Branchiostoma, 

 which Pallas placed among the Snails, from its great dissi- 

 milarity to ordinary fishes. The former has, in place of the 

 cranium, only a cartilage coiTesponding to the base of the 

 skull ; and the latter is deprived even of this, and the dorsal 

 cord extends to the end of the snout. The first has a single 

 fin, more or less divided ; in the other, the fin extends along 



