112 



HISTORY OF CRUSTACEA. 



CHAP. XI. 



nothing. In the second case the entire development of the 

 progenitors is also passed through ~by the descendants, and, 

 therefore, so far as the production of a species depends 

 upon this second mode of progress, the historical develop- 

 ment of the species will be mirrored in its developmental 

 history. In the short period of a few weeks or months, 



the changing forms of 

 the embryo and larvae 

 will pass before us, a 

 more or less complete 

 and more or less true 

 picture of the transfor- 

 mations through which 

 the species, in the course 

 of untold thousands of 

 years, has struggled up 

 to its present state. 



One of the simplest 

 examples is furnished by 

 the development of the 

 Tubicolar Annelids; but 

 from its very simplicity 

 it appears well adapted 

 to open the eyes of many who, perhaps, would rather 



67 



Figs. 65, 66, 67. 



1 Figs. 65-67. Young Tubicolar worms, magnified with the simple 

 lens about 6 diam. : 65. a without operculum, ProtoZa-stage ; 66. with a 

 barbate opercular peduncle, Filogr ana-stage ; 67. with a naked opercular 

 peduncle, Serpula-stage. 



a Fig. 65 is drawn from memory, as the little animals, which I at first took for young 

 Protulai, only attracted my attention when I remarked the appearance of the operculum. 

 which induced me to draw them. 



