258 s. WATASE 



Eacli fin-ray consists for the greater part of its length of two 

 similar pieces placed side by side and closely applied to each other. 

 At the thicker end, with which they come in contact with the inter- 

 hasmals, the two pieces diverge and present the shape of Y. In the 

 bay formed by the parted extremities a small bony nodule is inter- 

 cepted (Fig. 17). 



In the double form of the anal fin (Fig. 18), bony structures 

 similar to those of the single form are present in pairs. The observer 

 is at once struck wdth the close resemblance existing between the 

 paired inter-hœmal and the pelvic girdle. The anal fin also very 

 closely agrees in appearance with the ventral fin and one might think 

 that such a fish has a third pair of extremities (Fig. 3, PI. XA^III). 

 The double anal fin often makes a flapping motion and seems to 

 be capable of serving the same function as the ventral fin, although 

 on a much more limited scale. When the anal fin is partially paired, 

 the corresponding interhœmal bones alone occur in double state, while 

 the rest is unpaired and median. 



Primordial Fin-folds of the Gold-fish Embryo. 



The examination of gold-fish embryos shoAvs that the double 

 anal and caudal fins are already laid out in the primordial fin-folds. 

 In a gold-fish in which these fins are unpaired, the primordial fin-fold 

 is likewise unpaired as shown in Fig. 27 PI. XX. Where they occur 

 in pairs however the primordial folds are laid out as two longitudinal 

 thickenings along the ventral side of the post-anal section of the body. 

 Fig. 2Q represents an embryo taken from an egg three days after it 

 was laid. The ectodermal cells aggregate in two similar ridges (/,'/') 

 along the ventral side in the posterior position of the body, forming 

 the foundation of primordial fin-folds. A similar aggregation of 



