214 FORM OF ORGANS. 
subsequently became, began by being strictly symme- 
trical or regular, and that subsequent alterations were 
produced by inequality of growth or development. 
The researches of organogenists have, however, dis- 
pelled this idea of unvarying primordial regularity, by 
showing that in many cases flowers are irregular from 
the very first, that some begin by being irregular, and 
subsequently become regular, and even in some cases 
resume their original condition during the course of 
their development.1 Under these circumstances an 
artificial standard of comparison becomes almost an 
absolute necessity for the time being. 
Changes of form very generally, but not always, are 
accompanied with a change in regularity: thus a flower 
habitually bi-lateral may assume the characters of 
radiating symmetry and vwice versd. Increase or 
decrease of size very frequently also are co-existent 
with an alteration in the usual form. 
In the case of the arrangement of organs it 1s often 
difficult or impossible, in the present state of our know- 
ledge, to determine whether a given arrangement is 
congenital or acquired subsequently to the first de- 
velopment, whether for instance an isolation of parts 
be due to primordial separation or to a subsequent dis- 
union of originally combined organs, see p. 58. With 
reference to the changes in the form of organs, how- 
ever, it is in general more easy to ascertain the proxi- 
mate cause of the appearance, and thus teratological 
changes of form may be grouped according as they are 
due to, 1, arrest of development; 2, undue or excessive 
development; 3, perverted development; and 4, irre- 
gular development; hence the use of the followmg 
1 See Baillon, ‘ Adansonia,’ v, 176. 
