174 REPORT—1846. 
stood ‘analogous development,’ one cannot determine how much or how little 
it is applicable to the determination of homologies or to the definition of 
homologous parts. Dr, Reichert seems to have been unduly influenced by the 
idea of ‘analogy or similarity of development in the determination of homo- 
logous parts’ when he rejected the parietal and frontal bones from the system 
of the endo-skeleton, because they were not developed from a pre-existing 
cartilaginous basis*, or, because they could be easily detached from subja- 
cent persistent cartilage in certain fishes; the essential distinction between 
these and the supra-occipital in regard to development being, that whereas 
the cartilaginous stage intervened in the latter between the membranous and 
the osseous stages, in the other, usually more expanded, cranial spines, the 
osseous change appears to be immediately superinduced upon the primitive 
aponeurotic histological’condition. 
M. Agassiz seems, in like manner, to give undue importance to similarity 
of development in the determination of homologies, where he repudiates the 
general homology of the basi-sphenoid with the vertebral centrum, and con- 
sequently its serial homology with the basi-occipital, because the pointed end 
of the chorda dorsalis has not been traced further forwards along the basis 
of the cranium in the embryo osseous fish than the basi-occipitalt. But the 
development of the centrum of every vertebra begins, not in the gelatinous 
chord, but in its aponeurotic capsule, and it is in the expanded aponeurosis 
directly continued from the ‘chorda’ along the ‘ basis cranii’ that the thin 
stratum of cartilage-cells is formed from which the ossification of the basi- 
sphenoid, presphenoid and vomer proceeds. 
There exists doubtless a close general resemblance in the mode of deve- 
lopment of homologous parts ; but this is subject to modification, like the 
forms, proportions, functions and very substance of such parts, without their 
essential homological relationships being thereby obliterated. These rela- 
tionships are mainly, if not wholly, determined by the relative position and 
connection of the parts, and may exist independently of form, proportion, 
substance, function and similarity of development. But the connections 
must be sought for at every period of development, and the changes of rela- 
tive position, if any, during growth, must be compared with the connections 
which the part presents in the classes where vegetative repetition is greatest 
and adaptive modification least. 
Relations of homology are often not only confounded with those of analogy, 
but in some recent and highly estimable works on comparative anatomy the 
terms ‘ analogy’ and ‘analogue’ continue to be used to express the ideas of 
homology and homologue, or are so used as to leave in doubt the meaning of 
the author. Thus when we read in the latest edition of the ‘ Lecons d’ Ana- 
tomie Comparée’ of Cuvier, “ Les branchies sont les poumons des animaux 
absolument aquatiques,” t. vii. p. 164; and with regard to the cartilaginous 
or osseous supports of the gills, “elles sont, A notre avis, aux branchies des 
poissons, ce que les cerceaux cartilagineux ou osseux des voies aériennes sont 
aux poumons des trois classes supérieures,” Jbid. p. 177, we are left in doubt 
-whether it is meant that the gills and their mechanical supports merely perform 
the same function in fishes which the lungs and windpipe do in mammals, or 
whether they are not also actually the same parts differently modified in re- 
lation to the different respiratory media in the two classes of animals. The 
deeper-thinking Geoffroy leaves no doubt as to his meaning where he argues 
__ * Vergleichende Entwickelungsgeschichte des Kopfes der nackten Reptilien, 4to, 1838, 
pp. 212, 218. 
t Recherches sur les Poissons Fossiles, 4to, 1843, i. p. 127. 
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