Vol. 65.] ANNIVERSARY ADDRESS OF THE PRESIDENT. CXvil 



poverty in calcium-salt is a factor of the first importance in this 

 question. 



The absence of calcareous skeletons from the older rocks is, after 

 all, not inconsistent with what might be expected from the general 

 course or organic evolution. So far as the ontogeny is a recapitu- 

 lation of the phylogeny, so far it preserves for us the successive 

 adult states of the past. Successive adult states correspond to 

 existing larval stages, and larvae are either devoid of a skeleton or. 

 if they possess one, it is too minute for preservation. Nowhere, 

 even in sediments where the most delicate adult organisms have 

 left their trace, has the larval skeleton of an Echinoderm hitherto 

 been observed. 1 Yet what myriads upon myriads of these young 

 forms have continuously inhabited the Ocean since the Cambrian 

 time ! 



Hard parts develop not only for support but for defence also, and 

 it was possibly as a defence against predaeeous organisms that 

 Brachiopods and Lamellibranchs first became possessed of a shell. 

 Predaeeous animals do not appear, however, to have been very 

 common in the earlier Cambrian times. If we were to attempt to 

 classify the animal kingdom by function, one of the most fundamental 

 divisions would be into forms which feed by driving food-laden 

 water through their alimentary canal, strainers of an ' animated 

 soup ' as it were — Ethmophagites, and those which ingest their food 

 in a more wholesale manner — Thrombophagites. Nearly all the 

 Cambrian animals were ethmophagous, even the lowly Trilobites 

 may be assigned to this division : for, as Mr. W. K. Spencer has 

 pointed out to me, these creatures probably swam upon their backs 

 and drove food into their mouth by movements of the append- 

 ages, very much after the fashion of an Apus. The nature of the 

 worms, which were apparently the dominant organisms of the 

 time, is not sufficiently known to enable us to pronounce on their 

 habits. The earliest Annelid teeth described by Dr. Hinde are 

 found in the Chazy Limestone of the Ordovician System. 2 All the 

 great sub-kingdoms of the Invertebrata are represented in the Lower 

 Cambrian strata, but in every case by extremely primitive forms. 



1 In an earlier discussion of this subject I omitted to refer to W. K. Brooks 

 (Journ. Geol. Chicago, vol. ii, 1894, p. 455), who had previously expressed 

 similar ideas. The argument occurred to me quite independently, immediately 

 after the publication of my paper on Pucksia, Proc. Roy. Dublin Soc. vol. viii, 

 p. 297, read Dec. 19th, 1894. This must be my apology for unwittingly over- 

 looking this very important contribution. 



2 G. J. Hinde, ' On Annelid-Jaws from the Cambro-Silurian, &c.' Quart. 

 Journ. Geol. Soc. vol. xxxv (1879) pp. 351-69. 



