134 



HYPOTHESIS OF THE DEVELOPMENT OF 



is a perfect resemblance between the two. As far, however, as 

 we know of both, there is a very striking resemblance, and 

 every addition to our knowledge helps towards establishing a 

 complete one. On this point, one of the first of living natu- 

 ralists has lately thus expressed himself : " Nothing can be 

 more gratifying than to trace the close agreement of the general 

 results derived from the study of the structure of animals, with 

 the results derived from the investigation of their embryonic 

 changes, or from their succession in geological times. Let 

 anatomy be the foundation of a classification, and, in the main, 

 the frame thus devised will agree ivith the arrangement intro- 

 duced from embryological data. And again this series will 

 express the chief features of the order of succession in which 

 animals were gradually introduced upon our globed 



As examples and illustra- 

 76. tions : The Comatula, a 



free-swimming star-fish, (Fig. 

 48), is, at one stage of its 

 early progress, a crinoid 

 that is, a star-fish fixed upon 

 a stalk at the bottom of the 

 sea. It advances from the 

 form of one of the lower to 

 that of one of the higher 

 echinodermata. The animals 

 of its first form were, as we 

 have seen, among the most 

 abundant in the earliest fos- 

 siliferous rocks : they began 

 to decline in the New Red 

 Sandstone era, and they were 

 succeeded in the Oolitic age by 

 animals of the form of the ma- 

 ture comatida. The higher 

 Crustacea, as the crab and 

 lobster, at their escape from 

 the ovum, resemble the per- 

 fect animal of the inferior 

 order entomostraca, and pass 

 through the forms of tran- 

 sition which characterize the intermediate tribes of Crustacea. 

 The earliest Crustacea on the globe were entomostracous, and 

 1 Agassiz's work on Lake Superior. Boston, U.S. 1850. 



Crinoid state of Comatula rosacea 

 (Pentacrinus Europceus). 



