52 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 the 
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 may be that 
it is the impress of this ancestral free life which has given rise 
to the ancestral features in the development. 
