62 RADIAL REPETITION. [introd. 



tion as to what it might be if imperfect. Between the form in -3 

 and the form in -4 are intermediates possible? and if possible, do 

 they exist ? Now by choosing suitable species of regular flowers, 

 individual flowers may no doubt be found in which there are three 

 large segments and one small oue ; or two normal segments and a 

 third divided into two, making four in all. Such flowers are firstly 

 rare, while cases of perfect transformation are common. But be- 

 sides their rarity there is, further, a grave doubt whether they are 

 in any true sense intermediate between the perfect form in -3 and 

 the perfect form in - 4. After this again it must be asked whether 

 or no they do as a matter of fact occur as intercalated steps in the 

 descent of the form in -4 from the form in -3 ? To the last ques- 

 tion a general negative may at once be given ; for though there is 

 abundant evidence that Meristic Variations of many kinds and in 

 several degrees of completeness may be seen in the offspring of the 

 same parent, yet any one member of such a family group may 

 shew a particular Variation in its perfection, and the occurr ence of 

 any_jntermRdiate jjn_jhe_Jine_of_Desc ent is by jno means necessary 

 fiM^-the-^rodiigti on of the perfect Variation. 



To answer the former question, whether or no forms imperfectly 

 divided into four parts are in reality intermediate between those 

 in -3 and those in -4, a knowledge of the mechanics of the 

 process of Division is required. Such knowledge is as yet entirely 

 wanting, and discussion of this matter must therefore be prema- 

 ture. With much hesitation I have decided to make certain 

 reflexions on the subject, which will be found in an Appendix to 

 this work. These may perhaps have a value as suggestions to 

 others, though from their theoretical nature they can hnd no place 

 here. 



There is however another class of cases which are intermediate 

 in a different way. In the Tulip described above the quality of 

 division into 4 was present in all the floral organs. This is not 

 always the case, for a Meristic Variation may be present in one 

 series of organs, though it is absent in some or all of the others, 

 and this is a phenomenon frequently recurring. Nevertheless, 

 though only partially distributed, a Variation may still be dis- 

 played in its totality in the parts wherein it is present. The 

 parts of a single whorl, the calyx for example, may undergo a 

 complete Variation, while the corolla and other parts are un- 

 changed. In the same way single members of a radial series, as a 

 petal for example, may undergo a complete Variation while the 

 other members of the series are unchanged. The same will be 

 shewn hereafter to be true of animals also. 



For instance, the normal number of the parts in the disc of 

 Aurelia is four, but the whole body may be divided instead into 

 six or some other number of parts. Examples are also found in 

 which the parts of one-half or of one quadrant are arranged in the 

 new number, while the remainder is normal ; and, as in flowers, 



A 



