452 M ERISTIC VARIATION. [PART I. 



idt-s tin; caudal tin. tin- anal fin undergoes remarkable 



Fio. 141. Caudal and aiial fins of Gold-fish (Cyprinus auratu*). 



I. Normal tail, seen from side, r, dorsal lobe, d, ventral lobe. II. Abnormal 

 form divided a- far as the notochord. c' r', two ventral lobes, d' d', two dorsal 

 lobes. III. Abnormal form, tht> two ventral lobes, v' v', separate. IV. Pen- 

 ultimate vertebra of normal Carp (''. cm-pin). ..-, neural spine, h.s, haemal spine. 

 Y. Penultimate \<-it.'Kra of a Gold-fish with trilobed caudal fin. h'.s', double 

 li,-i uial .spine. VI. I Marram of transverse section through region of anal fin of 

 normal < luld-ti-h. VII. Similar section through a specimen having the anal fin 

 il. milled. /...-, interha-mul spine. /. r, tin ray. n, bony nodule, i.s', f'.r', n', corre- 

 spniidm" part- doubled. (After WATABB.) 



variation. It is either median and normal ; or it may be distinctly 

 (1'V 141. VII). 



are all stages of caudal and anal fins, intermediate be- 

 tween tin- normal and the completely paired states. Thus the 

 tail-fin with its IO\\<T portion alone in a double state, or the anal 

 h'n with cither its anterior or posterior portion double and the 

 remainder -in-le. is of quite common occurrence. These different 

 conditions of tin- two (ins coniliine in various ways in different 

 indi\ iilnaN t hns ^i\ ing rise to manifold varieties of form. 



This doubling of the tail-tin consists essentially in a longi- 

 tudinal splitting of the morphologically lower lobe of the tail. 

 The tir>i step in the process of doubling is seen in the case of 

 s in which there is a slight longitudinal groove in the 



