246 
EDWIN S. C400DRICH. 
The homology is independent of the number and ordinal 
position of the seg-ments which take a share in the formation 
of the organs. Any structure may apparently shift from one 
segment to another; and this is brought about neither by 
intercalation or excalation of segments, nor by redivision, nor 
by migration, but by a process of transposition. Organs may 
be homologous when they are composed of few or of many, 
of the same or of different segments, or are not segmented at 
all. There are degrees of homology : it may be general or 
more special, complete or incomplete. The homology of two 
organs is complete when all their parts have been derived 
from corresponding parts in a common ancestor. 
References. 
1. Bateson, W. — ‘Materials for the Study of Variation, ’ London, 
1894. 
2. Belogolowy, J. — “ Z. Entwickl. d. Kopfnerven der Vogel,” ‘Bull. 
Soc. Imp. des Natur. de Moscou,’ 1908. 
3. Bemnielen, J. F. van. — “ Ueber d. Herkunft d. Extremitaten- u. 
Zungenmuskulatur bei Eidechsen,” ‘ Anat. Anz.,’ iv, 1889. 
4. Brans, H. — “ Ueber d. Innervation der paarigen Extremitaten bei 
Selachiern,” ‘ Zenaisclie Zeitsclir.,’ xxix, 1895. 
5. Carlson, A. — “Unters. iiber Gliedmassenreste bei Scdilangen,” 
‘ Bihang till K. Svensk. vet.-Akad. Handl.,’ xi, 1886. 
6. Corning, H. R. — “ U. d. Entwickl. d. Kopf. u. Extremitatenmus- 
kulatm* bei Reptilien,” ‘ Morph. Jahrb.,’ xxviii, 1900. 
7. Froriep, A.— “ Z. Entwickl. der Wirbelsaule I : Beobacht. an 
Hiihnerembryonen,” ‘ Arch. Anat. u. Entwickl.,’ 1883. 
8. “II : Beobacht. an Saugethierembryonen,” ibid., 1886. 
9. Fiirbringer, M. — “ Zur Lehre v. d. Umbildungen des Nervenplexus,*^ 
‘ Morph. Jahrb.,’ v, 1879, 
10. ‘ Unters. z. Morph, u^ System, der Vogel,’ Jena, 1888. 
11. “Ueber d. Spino-occipitalen Nerven,” ‘ Festschrift z. s. Geb. 
Carl Gegenbaur,’ iii, 1897. 
llA. Gadow, H. — “ Myologie d. hinteren Extremitaten der Reptilien,” 
‘ Morph. Jahrb.,’ vii, 1881. 
12. Goodrich, E. S. — “ On the Development, etc., of the Fins of Fish,”’ 
‘Quart. Journ. Micr. Sci.,’ vol. 50, 1906. 
