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PROCEEDINGS OF THE 



[Tuly, 1857. 



animal. That such soft tissues couid leave their mark, was shown 

 by the specimen belonging to the Canada Survey mentioned above, 

 and that they should have been very much modified, in the course 

 of fossilization, was to be expected. 



There were also certain pretty constant differences between the 

 Graptolites and the parts of Echinoderm larvae, as at present 

 known to us, even in those cases where in the main they resem- 

 bled each other closely. Thus, the serratures of the edges, were 

 nearly always more numerous in the Graptolite, than in its nearest 

 analogues among the larvae of Echini. They also differed vastly 

 in size — the Graptolite being absolutely gigantic in proportion to 

 the Echinoderm larva, barely a line in diameter. To this, it was 

 to be replied, that in such a view as the suggested one, we are 

 comparing perfect fossil animals not with perfect ones of the 

 present age, as when, for instance, the scales and bones of a fossil 

 Lepidosteus are compared with those that now swim in our rivers, 

 but we are comparing perfect fossil animals, with the imperfect 

 immature representations of them which occur in the embryologi- 

 cal history of another very different group, which now, countless 

 ages after they have vanished from the scene of life, is still, if this 

 supposition be correct, yearly recording their former existence, 

 and sketching the details of their structure in a wonderful, if not 

 in a minute manner. If no fishes now existed in the seas, and 

 we were compelled to trace the relations of the parts in the fossil 

 fishes by a comparison with the larvae of frogs, we should find the 

 task still more difficult. If Pteropods existed only in the fossil 

 state, and we were to attempt to find their analogues, it would be 

 a long time before the larvae of Gasteropoda, would suggest them- 

 selves. The resemblance, as it stands between the Grap- 

 tolites and the Echinoderm larvae, is very great indeed, on the 

 supposition that the latter are embryonic representatives of the 

 former, and their great difference in size is certainly to be ex- 

 pected, on the ground, that the present suggestion is the true 

 one ; for nearly all embryonic forms are smaller than the perfect 

 animals, whose types they represent. 



There was, however, another argument which strengthened 

 this view, which Mr. McCrady thought proper to notice. Wher- 

 ever the young of an animal in its first stages has been found to 

 differ greatly from the adult in structure, as is the case of these 

 larvae when compared with adult Echinoderms, it has been found 



