172 Observations upon the Fossil Polypi of 



really different, but whose distinctive characters disappeared in 

 old age. But, in fact, the changes which we have detected in 

 the external conformation of the tegumentary cellules of the 

 living Eschara we have examined at different ages, occur also 

 in the fossil remains of these polypi ; and before we can pro- 

 nounce on the specific identity or distinction of these, it is of- 

 ten necessary that we should compare them in different periods 

 of their existence, a comparison which cannot always be accom- 

 plished, as the fragments found are often so small that they do 

 not contain cellules of different periods of life. 



Almost all the species of fossil Eschara of which good de- 

 scriptions or intelligible figures have hitherto been published, 

 belong to a very remote geological epoch, as they, for the most 

 part, belong to the chalk formation. These strata, however, 

 are far from being the richest in polypidoms of this genus, and 

 it is particularly in much more recent strata of the crust of the 

 earth that they are found in abundance. In certain strata, 

 whose formation is subsequent to that of the most recent ter- 

 tiary strata of the Paris formation, the number of Escharae is 

 so very considerable that, at the corresponding geological epoch, 

 these zoophytes appear to have contributed in our high lati- 

 tudes to the formation of immense banks in the same man- 

 ner, as at the present day, we see other polypi, creating reefs 

 and islands, in tropical seas. 



The combined observations of geologists and zoologists have 

 led to the conclusion, that in the creation of organized beings 

 the general tendency of nature has been to advance from the 

 simple to the more complicated. In the series of vertebrated 

 animals we regard this progress as indisputable ; it is probably 

 not so evident as it regards the series of the class mollusca, and 

 as yet we know too little of the articulata of the ancient world 

 to decide if the same law held good in this great class of ani- 

 mated nature ; but, be that as it may, the same tendency ap- 

 pears to exhibit itself in a very striking way in the structure of 

 the various polypi which have appeared at the surface of the 

 globe. 



In truth all our researches demonstrate that the Eschara and 

 neighbouring genera are of more complicated organization than 

 any other known polypi. But, amongst the numerous zoophytes 



