ORGANIC DEPENDENCE AND DISEASE 
63 
in these early presentments see that the fixation which led 
to recreancy was for a purpose distinctly advantageous to 
ease of living; that the creature became consolidated and 
set at a very early geological age. 
For the Lepad or goose barnacles we have very much 
the same sort of evidence. There are much elongated 
flat segmented barnacles in the Ordovician known as Lepi- 
docoleus. Others of this type occur throughout the Silu- 
rian and Devonian (Plumulites, Turrilepas, Strobilepis 1 ) in 
which the elongated shape and the regular fore-and-aft 
ranges of plates are retained, but the earlier form is much 
the simpler, as it has but two such ranges, one on each side 
and both symmetrical. Attachment in all of these is by the 
base, that is, by one end of the shell ; and we have expressed 
the belief that the whole stock to which these belong and 
which is represented by the existing Lepads arose from a 
like phyllopod ancestor to the Balanidae but through fixa- 
tion or cementation by the head, rather than the back; a 
fixation which gave a similarly favorable exposure of the 
feeding and breathing appendages, but also induced greater 
exposure to lateral stresses, which has resulted in a more 
numerous development of sutures and valves. This attach- 
ment, and consequently the career of the goose barnacles 
would seem to date from approximately the same geologi- 
cal age as that of the Balanidae and, as we have said, to 
have come out of the same free and independent crustacean 
stock. 
i These have been commonly accepted as Cirripedia and while we are grant- 
ing that the probabilities seem in favor of this interpretation, there are features 
of structure which suggest the scaled annelids. This comparison has not been 
closely carried through. 
