192 Dr. A. Giinther on the Immature State 



great mobility which the lateral parts of the head possess. 

 Whilst Diiben and Koren preferred to figure their specimen 

 in the most depressed (and perhaps the most natural) position, 

 Dr. Riippell had his specimen compressed as much as possible, 

 in order to be able to show the insertion of the ventral fins 

 in a lateral view of the fish : this accounts for the difference 

 in general form. In the Mediterranean fishes, the first ray 

 is comparatively longer than in the Scandinavian, and termi- 

 nates in two compressed flaps, which, perhaps, are only a 

 more developed form of the transverse cylindrical knob in L. 

 eurypterus. How variable the length and the shape of the 

 fins and of their appendages are, even in specimens of the 

 same size and age, is fully proved by the two Scandinavian 

 specimens, one of which has the ventral twice as long as the 

 other. Further, the anterior dorsal spine, whether it serve as a 

 bait to attract other fish (which is by no means improbable), or 

 as an organ of touch, is constantly exposed to injury from the 

 delicacy of its structure as well as from the peculiarity of its 

 function. Finding it, however, sometimes very long and fully 

 developed in old fishes, we cannot hesitate to assume that it 

 is reproduced when lost ; and this appears the more probable if 

 we consider that portions of the fin-rays as well as of the barbels 

 are reproduced in other fishes. We therefore cannot be sur- 

 prised, or think it a matter of any importance, when we find the 

 anterior dorsal spine of different length and its tentacle of different 

 shape ; both are subject to an indefinite number of accidental and 

 individual changes, besides the constant differences by v;hich the 

 young fish is distinguished from the old one. Finally, another 

 source of discrepancy in the descriptions and representations of 

 the authors named is the alteration which the fishes undergo by 

 their preservation in spirits: a part, or all, of the tender fila- 

 ments in which the rays terminate are easily lost, and the fins 

 themselves are considerably shrivelled up ; so that it would be 

 impossible to repi'oduce a figure of the present Frankfort speci- 

 mens similar to that which was made from them when they were 

 quite fresh. The ventral fins are still longer in the Mediterra- 

 nean fish than in one of the Scandinavian specimens — being, 

 with the filaments in which the rays terminate, as long as the 

 whole fish. Diiben and Koren believe that the length of the 

 ventrals indicates a sexual difference. I cannot share this opi- 

 luon, which is contrary to what we observe in other fishes. If 

 there are external sexual differences in a species, they do not 

 appear before the individuals approach maturity : the young 

 male and female of Callionymus lyra are perfectly alike ; and the 

 dorsal and caudal fins begin to grow, and the bright colours to 

 make their appearance, only in male specimens of more than 6 



