Chap. XXVI. AFFINITY OF HOMOLOGOUS PARTS. 341 



Hunter and others Lave observed lizards with their tails repro- 

 duced and doubled. When Bonnet divided longitudinally the 

 foot of the salamander, several additional digits were occasionally 

 formed. But neither these cases, nor the perfect series from a 

 double monster to an additional digit, seem to me opposed, to 

 the belief that corresponding parts have a mutual affinity, and 

 consequently tend to fuse together. A part may be doubled 

 and remain in this state, or the two parts thus formed may 

 afterwards through the law of affinity become blended ; or two 

 homologous parts in two separate embryos may, through the 

 same principle, unite and form a single part. 



The law of the affinity and fusion of similar parts applies to 

 the homologous organs of the same individual animal, as well as 

 to double monsters. Isidore Geoffroy gives a number of in- 

 stances of two or more digits, of two whole legs, of two kidneys, 

 and of several teeth becoming symmetrically fused together in 

 a more or less perfect manner. Even the two eyes have been 

 known to unite into a single eye, forming a cyclopean monster, 

 as have the two ears, though naturally standing so far apart. 

 As Geoffroy remarks, these facts illustrate in an admirable 

 manner the normal fusion of various organs which durino- an 

 early embryonic period are double, but which afterwards always 

 unite into a single median organ. Organs of this nature are 

 generally found in a permanently double condition in other 

 members of the same class. These cases of normal fusion 

 appear to me to afford the strongest support in favour of the 

 present law. Adjoining parts which are not homologous some- 

 times cohere; but this cohesion appears to result from mere 

 juxtaposition, and not from mutual affinitv. 



In the vegetable kingdom Moquin-Tandon 5 gives a long 

 list of cases, showing how frequently homologous parts, such 

 as leaves, petals, stamens, and pistils, as well as aggregates of 

 homologous parts, such as buds, flowers, and fruit, become 

 blended into each other with perfect symmetry. It is interesting 

 to examine a compound flower of this nature, formed of exactly 

 double the proper number of sepals, petals, stamens and pistils, 

 with each whorl of organs circular, and with no trace left of the 



5 ' Teratologie Veg.,' 1841, livre iii. 



