ANIMAL PEDIGREES 21 1 



the more recent formations, is prodigious; and what 

 we have to do is to make the most of the material 

 already accumulated, rather than to fold our hands 

 and idly lament the absence of forms that perhaps 

 never existed. 



It is true that with all groups the chances are 

 not equal. But by judicious selection of groups in 

 which long series of specimens can be obtained, 

 and in which the hard skeletal parts, which alone 

 can be suitably preserved as fossils, afford reliable 

 indications of zoological affinity, it is possible to 

 test directly this alleged correspondence between 

 the palaeontological and embryological histories; 

 while in some instances a single lucky specimen 

 may afford us, on a particular point, all the evidence 

 we require. Many serious attempts have already 

 been made to work out in detail this comparison 

 between fossils and the developmental stages of 

 living forms, and the results obtained are most 

 promising. 



Following the lines laid down by his father, 

 Alexander Agassiz has made a detailed comparison 

 between the fossil series and the embryonic phases 

 of recent forms in the case of the Echinoids or Sea 

 Urchins, a group peculiarly well adapted for such 

 an investigation, as the fossil representatives are 

 extremely numerous and well preserved, and the 

 existing members well known and comparatively 

 few in number. Agassiz shows that the two 

 records in this case agree remarkably closely ; 

 more especially in the independent evidence they 

 give of the origin of the asymmetrical forms from 



