92 ADAM SEDGWIOK. 



higher animals it is the early stages of development which 

 have the greatest interest for us^ the later stage having been 

 added at a time when, as now, the immature stages of free life 

 were but little marked, and consequently there was but little 

 chance of the incorporation of any ancestral features in tlie 

 embryonic development. It also helps us, I think, to under- 

 stand why the most interesting of the ancestral embryonic 

 features were related to the passage from the aquatic to the 

 terrestrial condition, because when this took place in phylo- 

 geny there must have been a most pronounced aquatic larval 

 stage, such as we find to-day in Amphibia. 



Appendix. 

 Mr. J. J. Lister has pointed out to me as confirmatory of 

 the views set forth in the preceding pages that there is at least 

 one exception to the rule that animals produced by budding 

 show no ancestral rudiments in their development, viz. the 

 sexually mature medusoid spore-sacs. These organisms present 

 in their development traces, as is well known, of many organs 

 which they must formerly have possessed in a functional con- 

 dition, e. g. the umbrella cavity, the marginal tentacles, the 

 circular canal, &c. ; but, as Mr. Lister points out, these spore- 

 sacs differ from other buds in this important fact that they 

 have most undoubtedly had quite recently a free life during 

 the maturation of the generative products; and it maybe that 

 it is the impress of this ancestral free life which has given rise 

 to the ancestral features in the development. 



