452 



MERISTIC VARIATION. 



[part I. 



Besides the caudal fin, the anal fin undergoes remarkable 



Fig. 141. Caudal and anal fins of Gold-fish (Cyprinus auratus). 



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

 form divided as far as the notochord. v' v', two ventral lobes, d' d\ two dorsal 

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

 ultimate vertebra of normal Carp (C. carpio). n.s, neural spine, h.s, haemal spine. 

 V. Penultimate vertebra of a Gold-fish with trilobed caudal fin. h'.s', double 

 haemal spine. VI. Diagram of transverse section through region of anal fin of 

 normal Gold-fish. VII. Similar section through a specimen having the anal fin 

 doubled, i.s, interhaernal spine. /. r, fin ray. n, bony nodule. i.s',f'.r', n', corre- 

 sponding parts doubled. (After Watase.) 



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

 paired (Fig. 141, VII). 



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

 tween the normal and the completely paired states. Thus the 

 tail-fin with its lower portion alone in a double state, or the anal 

 fin with either its anterior or posterior portion double and the 

 remainder single, is of quite common occurrence. These different 

 conditions of the two fins combine in various ways in different 

 individuals thus giving rise to manifold varieties of form. 



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

 tudinal splitting of the morphologically lower lobe of the tail. 

 The first step in the process of doubling is seen in the case of 

 gold-fishes in which there is a slight longitudinal groove in the 



